Unusual behavior?

Ricky Bobby has been acting strange for the past hour or so. He's going to the corner of the room and laying down and letting out a couple of meows that sound kind of like whimpers. He's worrying me. He'll stay in that corner and lay down. It's a dark corner and i know cats like to hide and be left alone when they're not feeling well, that's why it's worrying me. I don't believe he's had anything out of the norm to eat, right now he's eating Blue Wilderness. I'm just worried about him. I got his ball and we played fetch for about 20 minutes(after the 1st time I noticed him going to the corner, I wanted to see if he was up to playing) and he played like he normally does. I haven't noticed any changes in his litter box behavior either. I wonder what's bothering him. What should i look out for?

Things I always look for include change in eating, sleeping, playing, and litterbox habits, hiding under furniture or in the closet, not coming around when it's normally time to eat, general lethargy, dehydration, tenderness in a certain area when petted/groomed, change in gum color, change in eye color (the white part), and change in behavior. If this has just started today, I'd keep a close eye on him and if he doesn't seem to be back to his normal self in the morning, call the vet.