My endometrioma was discovered when I was scanned due to bleeding at "8/9 weeks" pregnant. The embryo had actually stopped developing at around 5 weeks and the bleeding was the start of a miscarriage. 
Obviously I was devastated and wanted to start ttc straight away, fortunately I was seen by an endometriosis specialist very quickly who explained that with such a large cyst I would need to have it surgically removed before I started ttc again. If I hadn't miscarried then he would have operated during my 2nd trimester, when the risk to the foetus was lower.
I had the cyst removed by key hole surgery and was lucky to not lose my ovary. The consultant also found small patches of endo elsewhere but thinks that it's unlikely it will cause me problems in the future (and so far he's right!) It wasn't a complete shock to be diagnosed with endo - I had suffered symptoms in the past but they hadn't been severe enough to push my GP for a referral to investigate further.
I was in quite a bit of pain after the operation, particularly because I thought I was ok so declined anything stronger than paracetamol to start with, a decision I regretted once the post-operative suppository (codeine or similar?) wore off. Much better to take all the pain killers offered and keep topped up!
After a few days paracetamol was fine for the pain and I was able to manage taking care of my toddler, although we did take things easy. I'd arranged to have 6 weeks off work, but I'm a teacher so would be on my feet virtually all day and needed to be at my best! I could easily have returned to an office-based job sooner. I must have been feeling better 4 weeks after the surgery as I had a positive pregnancy test the week I returned to work, the result of which is my 3 yo DS2. 