Cramps after embryo transfer

Just had a question

Yesterday was my embryo transfer day for a blastocyst

I am 36 and had 2 normal labour before but going for pgd this time

After transfer i kept resting on my back and didnt move for half and hour but my head was slightly lower than my body

After half an hour i got severe cramps just like pregnancy cramps that went to my back causing severe back pain then i started to have low blood pressure and going to faint

I just got up on a chair all the syptoms got milder and totally releived after going to the toilet

Are these sypmtoms of full urinary bladder as i was in full bladder or is it a uterus contraction as i am very worried anything might happen to the embryo