Sick kitty, I think

So Gus is worrying me lately.  For the last two days he has done nothing but sleep.  Now before you smart aleks out there tell me that's what cats do, I'm telling you it's not normal for him.  He usually spends the time from when we get home until we go to bed running around, playing, doing hijinks, and generally tearing it up.

Saturday, he lay on the couch on a fuzzy blanket the entire day.  He only got up to eat and use his toilet.  Then he slept in bed with me all night.

Sunday, he lay on the couch on a fuzzy blanket the entire day.  He only got up to eat and use his toilet.  I did try to tempt him with his favorite toy, which is a string on a stick with feathers.  Usually I touch it and he immediately comes running.  Sunday, his ears perked up and he played half heartedly for a few minutes, then he couldn't keep his eyes open and got back on the fuzzy blanket and went to sleep. He slept with me all night.

He did follow me into the bathroom when I had a shower on Sunday. But rather than meow at me and check that I was still behind the curtain, like he usually does, he fell asleep in the sink.

If he doesn't greet me at the door today and act like his normal, crazy self, he's going to the vet.  

Secretly, I think he's going through a growth spurt, but I'm still feeling very worried. Give the dude a prayer if you are reading!

***Update***He was fine when I got home.  Back to his crazy, sweet, and loving self!