Nausea/ vomiting

Over the past month or so, I will get sudden nausea and start throwing up. I get it about once a week, always at night before bed, it comes on suddenly, seemingly with no cause, and I will throw up for about 5 minutes straight. Afterwards, I feel completely fine. I have no other symptoms of a bug or anything. No change to my diet, medication, or anything. I'm not pregnant.

Anyone know what could be causing this?