What is up with me?!?!?

im 39 weeks pregnant and i woke up this morning feeling fine (few period like cramps but i've started getting used to that lol) then out of no-where i started feeling nauseated and i went to the toilet and had really bad diarrhea (sorry TMI) the nausea carried on then i started feeling vey shaky then i started sweating. started to feel really weak. this carried on for another 20 minutes...............then i felt fine again. anyone have any idea what this could have been? i have not eaten anything that could have made me ill