I'm having this problem too, about three times a week. No nausea and only a few seconds of warning. I'm beginning to think it's associated with my heartburn/ acid reflux. Finally put a call into the doctor about it.My constant sickness went at 15 weeks but as of last Thursday (19wks) I have started to randomly throw up. I get no warning, I don't feel nauseous but about 10 seconds before I throw up I start to heave. I know what that means now and it goes after 1/2 hour. It can happen once a day or it can happen several times a day and it did it through the night and woke me up several times.