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It sounds like he may be having a bit of a stress response in his gut from the change in scenery with you leaving. That can stress out some cats and cause vomiting and diarrhea. It will usually resolve within a couple days on it's own.
To help it resolve, make sure he's eating and drinking normally. You can also give 1 teaspoon of canned pumpkin 2-3 times daily to help normalize his bowel movements. The extra fiber will help the colon. This should resolve nicely on it's own, though. It doesn't sound too serious.
I hope this helps, let me know if you have any other questions.