Vomiting Returning in 2nd a Trimester?

Hi ladies, so I had severe morning sickness all 1st trimester and into my 2nd trimester. At about 16 weeks it finally stopped and I've been feeling great for 2 weeks. Now I'm 18w2d. Out of nowhere yesterday morning and this morning, I wake up, cough, run to the bathroom and vomit stomach acid or whatever as my stomach's empty from just waking up. No warning. No preceding nausea. Has this happened to any of you after you were feeling better? Should I be worried at all? Thanks.