I've only had it once during the 4 month sleep regression. I was honestly so stressed out and unhappy I thought he would be genuinely better without me, because I wasnt a good enough mum to him. So in that sense I regretted having him then. He just didnt sleep at all and was so miserable and nothing I did seemed to work. I was a mess.
Luckily it got a lot better! But I wonder how common this is? It's almost taboo to talk about, but think it would help mums if they can talk about it more. It's so hard and even though you love them to pieces, these feelings happen.