I had one 20 years ago. I'd been in a short relationship with a friend, I only found out about 8 weeks after we'd ended it - we decided we were better as friends, and he was seeing someone else by then (who he is still with!) I never told him.
The procedure itself was very straightforward. I was only in hospital for a few hours. The thing I really remember is having a sneezing fit as I was coming round from the anaesthesia (which is apparently really common) and feeling quite nauseous, again from the anaesthetic. I was given an anti-emetic and that helped.I felt very weak and wobbly, but was given pain killers for the first 48 hours, so just felt spaced out and very tired more than anything. after that I ached a bit, but nothing awful.
I know that I did the right thing, at that time I did not want to be a mum, way too selfish and irresponsible.
I did have another unplanned pregnancy around 5 years later, I'd only been with my then BF (later DH) for about 10 months, but I knew at that point I wanted to keep the baby, my wonderful DD! I do think it was because of the termination that I was so sure - I was in my mid 30s by then and figured if nature was so determined I should have a baby despite my best efforts, then maybe it was meant to be!
I certainly don't regret it, although I do think about them around the would-be birthday and wonder what they would have been like.
I knew it was what I wanted to do, but if you are not sure I really recommend speaking to the GP, or the clinic you are booked in to. They eon't tell you what to do, but the can help you to sort out your own thoughts. Sending you love and strength