Year old Male cat has very mild convulsions, possible hyperesthesia?

My year old male cat, Zuko, is unfixed, and has always been quite a hyperactive guy. I've posted before about how erratic his behavior has been in the past. Luckily, he's calmed down a bit as he's gotten older, but I've noticed something new in the last several months - he sort of has these convulsions, but only when he's laying down/resting/sleeping. It seems to come from his flank/hind legs region, but you can see his whole body convulse, especially his head. It's not twitchiness, because it's not sporadic, it's rhythmic and constant any time he lays down, but it doesn't appear to be hurting him at all. Sometimes when he's hyper he will bite his legs or tail, which is a symptom of hyperesthesia, but it seems like cats who have that tend to kind of freak out and bite themselves when they twitch/convulse, but he usually just ignores it. It's kind of hard to see just by looking at him but i noticed it because he was sleeping on my leg one night and i could feel it, and from then on i started watching him and feeling his body to see where it was coming from. It might not be related, but he's also EXTREMELY hormonal, he humps the clothes on the floor like 10 times a day. and he almost always drags them out to wherever we are to do it. He also licks his crotch ALL the time, whether he just got done humping something or not. Other than that he's just a hyper little guy (not that he's little, he's a big cat).

If anyone has any opinions, i'd be interested to hear them. I'm not really all that worried cause it doesn't seem to be causing him any problems, I'm just curious about it.

Is there a reason you don't want to fix him? Is he inside only?

The humping, licking, and excess energy are related to his hormones, which are probably quite uncomfortable for him.

Yes, he is inside only, and there isn't a reason why I haven't fixed him other than that we fell on hard times and couldn't afford it and it fell on the backburner what with all the confusion with some billing mistakes with our landlords consistently blah blah... which i feel very guilty about, and plan to rectify soon. There are no discount spaying/neutering programs where I live, I check every month. But i worry that i'm gonna have a much bigger vet bill to save for with these convulsions, because they're getting worse, so I need to start saving now.... 

I am positive this hasn't got anything to do with him not being fixed though. This is strange. Just now, i didn't even know he was in the room, I was watching a video on my laptop in bed, and then i start to feel the bed shake and vibrate, and I know that he's there. I look and it is much more visible than normal. I have read about twitchiness, shakiness, breathing problems, erratic behavior, etc in cats, but this isn't shakiness or twitchiness, it's rhythmic convulsions. That's the only way I can describe it. 

I hope someone happens by this thread that has had a similar issue because I have not been able to find any information that sounds similar to what he's got.