Was this a virus? (warning re: details)

B spent the night at MIL's last night.  DH and I both taught a class on Tuesday nights (last night was the last class), and he had an early morning meeting in the east bufu (literally...).  Anyway, he was at MIL's from about noon yesterday until ~3:45 today. 

Last night he went to bed at 9:40...  a little later than normal, but with him at grandma's it throws things off.  He woke up at 11:40 THIS MORNING.  So he slept ~14 hours.  Keep in mind he doesn't nap.  He wasn't particularly hungry when he got up.  He drank a little water, had a cereal bar and some crackers later. 

He played like normal, maybe a little more intense as he was running/chasing after a ball for a while.  ~2 he puked.... it was really clear, not a lot of food in it.  That's not surprising given that he slept late and didn't eat a lot.  After that, he fell asleep and was in and out of sleep for the next hour or so.   I got there around 3:15 and he was laying on the floor.   His eyes were glassy and while he didn't feel warm he was definitely lethargic.  I gave him some G2 gatorade mixed with water, he perked up a little, and we went home.  He vomited twice during the car ride.  We got home about 4:15.  He spent the next 2.5 hours or so lounging on the couch in a fairly lethargic state...  no fever, but no appetite either.  He drank a little more G2/water mix and ate a small cracker. 

About 7 tonight he was starting to become more playful.  He asked to take a bath (thank goodness) and seemed completely normal before we went to bed.  I gave him some food around 8- he picked it out.  Nothing too heavy, but substance.  By the time we finished our bath, he seemed completely normal. 

So.... if you've read all that- virus?  something he ate?  thanks