my kitty is about eight months old, and he's been on practically the same diet his entire life. we switched him from wet to dry food a few months ago, but he's pretty much always eaten only organic kitty food. he's been on the same dry food for about a month or more. he's mostly an indoor kitty, but goes out for an hour or so occasionally. we woke up this morning and found kitty vomit in the living room that had pieces of his food in it. an hour or so later he had vomited again, but it was mostly liquid. we later discovered vomit that may be from much earlier, possibly last night, and it is mostly food. he's being really lazy, and he's usually playful, but not today. he looks tired, but isn't sleeping right now. he did go outside yesterday, but not for long. should we take him to the vet? what could be wrong with him?