Vomiting and length of time food is in stomach

[Lernermichelle]

When Simon threw up an hour or so ago, after I picked him up and accidentally squeezed his stomach, there was undigested food in the vomit from about 18 hours ago-- some fancy feast chunks he ate at about 7 pm last night. I thought that food only takes about 3 hours to pass through the stomach.  Is it normal to still have some food in there from yesterday, or does this mean there is some new problem related to food moving through his system? Or is his digestive system shutting down?  Someone on the lymphoma list serv said her cat vomits 2-5 days after getting the kind of chemo that Simon got on Thrusday, so I am hoping his vomiting is just a passing side effect, but the food from yesterday worries me. After vomiting he got very purry right away again, and  has been asking for belly rubs non-stop until falling asleep a minute ago next to me on the bed, where I am writing on a laptop. I am not sure whether to offer him more food when he wakes up or not. He ate a little this morning, a very smal amount, but I am sure that must have come up when he threw up.
Thanks if any of you know,
Michelle