Happens to me too, badly enough to have me in and out of hospital trying to figure it out. It's been put down to stress induced migraines which present themselves mostly as sickness - maybe if you treat it as a migraine (i.e. peace and quiet, some paracetamol and light food) it'll ease it. I take cyclizine (prescription only) sometimes when I feel particularly sick, often when taking exams, going back to college after a break, breaking up with someone etc. I couldn't offer you any advice for stopping feeling sick, but I find that exercising some mental control over it helps as it seems to be an emotional rather than physical problem, so I tell myself I won't be sick and eventually the nausea fades. It might be worth going to your GP and asking to be referred for blood tests. When I go through a patch of stress/sickness, the levels of serum prolactin (pregnany hormone - morning sickness) go right up. If this is happening with you too, you could get some prescription drugs to combat it.