So, I haven't had any nausea since right around 11 weeks, and all of a sudden tonight I feel like…

So, I haven't had any nausea since right around 11 weeks, and all of a sudden tonight I feel like crap! Intense nausea coming in waves, and I haven't thrown up, but I also have dealt with nausea a lot before pregnancy, so I have trained myself to never throw up unless I want to. whyyyyy has this symptom come back?!?