Cat suddenly not as active anymore

My boy cat is a little over a year old. He and his sister went in for their vaccinations two and a half weeks ago (rabies and FVRCP). My boy was a little tender where he got the vaccines for a couple of days, but then he bounced right back and was completely normal. About three days ago, he started eating less. He was still interested in his food, but before when he was literally running to it and gobbling it up, now he slowly meanders toward it and slowly eats it, sometimes not eating all of it until I bring him back to it to finish.

He's also not playing as vigorously as he normally does. He'll still be somewhat interested in play, but no where near as much energy as what I'd normally see. The day before he started acting kind of odd, he and his sister were tumbling around like normal. She's completely fine, but he isn't. He's also sleeping and laying down more often too. Outside of him just being more low key, he still likes being picked up and held, getting belly rubs, doing tricks for treats. His bathroom habits have not changed and while he doesn't seem as excited about his food as he used to be, he still eats all of it.

I'm a bit worried that there's something bothering him and it's been going on for three days now. But outside of him being more "relaxed", he doesn't show any other signs of anything being wrong. It seems a little late in the game for him to be having a reaction to the vaccines, but the vet did say to watch him for at least 30 days after the shots. Mostly they were worried about monitoring the injection sites but those have been fine.

I just want to get some ideas to see if anyone has a similar experience before I take him in to see the vet. He doesn't like going there and it really stresses him out, but this has been going on long enough that a trip to the doc might be inevitable.

I hope that I'm not passing on bad info, but I've heard that some cats react to vaccines by getting slightly ill, just as a flu vaccine would give some people symptoms of a flu. Typically they'll be achy and groggy. Definitely call your vet ASAP to verify this though! The late reaction is kinda weird, but maybe it's just a strange immune system thing. I'm sure the vet understands the difficulty of traveling with a cat and would provide counsel via phone since this concerns his vaccines. Good luck!

The "flu like" symptoms after vaccinations are usually right after...like within a 24 hour period or so

Is it starting to get hot where you live?  This could be the reason why your little one is not as active and not wanting to eat as much.  Some cats react to the heat, even though they may live completely indoors and the temperature stays the same with air conditioning.  Mine slow down.  Plus he's coming out of his kitten stage and may just not be as full of energy once that happens.  This could all be coinciding at the same time.

To be on the safe side, call your Vet and tell him what's happening and see if they think it's a concern.

It is getting hot here, and maybe that has something to do with it. My kitty is 100% indoors, eats only wet food (Tiki Cat and Weruva) and only the chicken or turkey varieties. I noticed today that he's been walking a bit tenderly on his back two hind legs, which is where he got the vaccinations. That would lead me to think it's related to the shots, but he was honestly fine two days after the shots until now. I don't know if this is just him growing out of his kitten crazies, it seems to have come on a little too suddenly.

I'm going to give the regular vet a call tomorrow. I took him in to a vet that was open on Saturdays yesterday, that we don't see often and keep on hand for weekend emergencies. They felt his legs, took a stool sample, took his temperature and they said everything looks OK. I don't know what it is so we'll see. He's still sluggish today, still eats all his food but very slowly, and has no interest in playing, he used to like climbing to the top of his cat condos but he seems to be avoiding jumping or doing anything vigorous with his hind legs. He hasn't been doing much of anything other than napping, eating and going to the bathroom. His bathroom habits are still normal for him, no litterbox issues. I'm stumped. I'm just really worried because he's behaving very unlike himself.

Thank you for the advice msgreenjeens and rachelleb. I'll update when I know more.

Took him in to his regular vet. They felt his hind legs and remarked that they seemed stiff and he is reluctant to stretch them out all the way. They did a blood test that came back normal, listened to his heart and lungs and they seemed normal. His temperature was also normal. Ultimately, they weren't able to figure out what it was. His injection sites have gone down so they aren't a concern either.

We got Metacam for the pain and since taking it, he has seemed to feel a little better. Still not running and jumping like normal but he is at least walking around a bit more. He's still sleeping more than usual, seems lethargic, and now he's only eating about half his food and leaving the rest. I'm at a loss for an explanation and very worried. I have a followup appointment with the vet for XRays to try and get to the bottom of this in a few days time.

I would encourage you to not give him Metacam.  Do a search on this site for serious side effects.  I would ask for a different pain medication. 

I'm wondering if they nicked a nerve or something when giving the shot.  Just trying to help you figure things out.  Also, did they feel his tummy and make sure his tummy wasn't inflamed and/or his bowels inflamed?

Thanks, stephanietx. I'll give his vet a call and request a different pain medication tomorrow when they open. I still wonder if it was the vaccines that caused any of this, but it seems like three weeks after vaccination, he would have presented any issues like a nicked nerve or lethargy immediately after receiving the shots. Outside of the shots, I haven't changed anything and nothing has changed in his food, environment or schedule.

Before being given the metacam, he seemed to be getting worse. Not even interested in his food anymore, barely even walking and just preferring to lay on my bed and sleep. He's been stretching his legs a lot and licking at his hind legs which is why I and both vets think it's his hind legs bothering him. Before this all happened, he used to purr every single time I pet him, but I haven't heard him purr since it started getting worse. He also used to love jumping on my dining table and staring at me while I ate. I feel like all it is doing is getting worse--whatever it is. Of course, if I do a search for his symptoms, some really scary stuff shows up, not sure if any of it is even useful because he has symptoms of this, but not of that and I'm not a vet anyway. I just wish my kitty would go back to normal. He used to drive me crazy with his antics, and now all I want is for him to go back to driving me crazy again.

Just going to post an update because I know how frustrating it is if there's no closure to a thread like this. My kitty started feeling and acting more like himself four days after my previous post. He had XRays which revealed nothing, but his temperature was a little on the high side.  A day after that, he started slowing down and being lethargic again. Now he's got persistent diarrhea, going three to five times a day, but his legs are working better now in that he doesn't walk on them tenderly anymore.

He's on metronidazole for the diarrhea with a course of probiotics once he's done with the metro. It has helped him in the past and he doesn't have any side effects from it, so we'll see if this helps him now. We still don't really know what's wrong with him. He's had multiple tests done on his stools, a blood test, and pretty much everything we can think of. At this point, we're suspecting something elusive and hard to detect like giardia or tritrichomonas foetus. I've managed to get him to start eating again at least, but he's still sleeping and behaving irregularly.