This morning we were on our way out and my son was whimpering and then vomited all over himself and in the car. We got back and he slept for about 4 and a half hours and after waking seemed really happy, had some water and then about 20 mins started whimpering again, hitting his head like it was painful and about 10 mins later vomited. He's chilled out since being sick and happier but has little energy. He doesn't have a fever, rash or diarriah so I'm confused if it is a virus or something else. Any ideas what it could be?