yes, I had the same thing, "collection in the morrisons pouch" or something like that was written in my discharge papers.
I lost a lot of blood, and was still losing it internally until day 3 when they realised I should I have been unconcious, (after transfusions that didnt seem to make a difference) had an emergency ultrasound and that was where I was told the blood "fluid" was going.
I had to go back for internal ultrasounds to check on the lining of my uterus a few weeks after birth, was given anti biotics for suspected infection (low grade fever and pain in the area, as well as thickening of the endometrium)

Mine was like yours in that it was numb, to be honest, that area now is still numb.
If you have any pain or develop a fever, please ring/see the hospital ASAP.