My obstetrician suggested you can have BH without realising it, because they're not always apparent but your uterus is still doing what it's supposed to do.

I didn't notice them at all until I felt one when I was lying on my side on the couch watching TV one day, and then I became aware of what they were so I started noticing them after that ... but only in certain situations. I only notice them when I am out walking or lying on the couch watching TV.

Actually, the other day I had one when I just sat down to go to the loo. That was strange, it prevented me from doing my business until it passed.