With my first I had braxton hicks for two weeks before hand so when I went into labour I didn't think any different my water hadn't broken and the pain was the same I'd been going through it wasn't untill my mum saw me the next morning that she realized I was in labour 4 hours later I gave birth all told i was in labour for 12 hours and 48mins most of it without realising
Yes it's possible I was having them at 33 weeks while at my weekly scan. They sent me to labor and delivery to stop the contractions but I didn't feel a thing
Yes it is very possible, I have had it happen twice. My first I was past my due date and my plug started coming out, called the Dr they told me to go in and get checked out. They asked if I was having any contractions, told them no. The nurse turned right around and asked me again after hooking me up to the monitors and asked again because the monitor was saying I was having strong, consistent contractions. I was only feeling very mild back pain. With #2 I only went in because I was having a scheduled c-section. For about 72 hr leading up to the c-section I had maybe 3 in an hr and then several hrs apart before I had any more. I only know I was in labor because when the Dr started the c-section right away she asked if I had been having any contractions because my cervix was extremely thin. She told my husband that if we wanted a 3rd child we had to wait to start trying till the day after #2 turned one to give my body time to heal properly.
I went in labor with my daughter full term and thought I was just having braxton hicks contractions. About 5 hours latter I was holding my babygirl. So yes it's possible to be in labor with painless contractions.