First of all, congratulations!
Secondly, that was my biggest fear when i was doing hypnobabies. I heard so many people say that they didn't experience pain and that the typical physical/emotional cues during labor that tell you it's time to get to the hospital/bc just aren't there when you do hypnobabies and I so worried I'd end up with an unplanned homebirth or giving birth in the car ride there (I was an hour and 15 minutes from the bc). But, I had a 28 hour long labor with baby #1 so I figured I was safe. That said, my second baby's labor was less than 3 1/2 hours. I really did not know I was in labor and did not think I needed to go into the birth center (despite my contractions being 2-3 minutes apart). I never had any that were further apart than that - I just woke up that way, but they just felt like braxon hicks and werne't painful and were only lasting 45 secondss. I didn't even wake my dh up for another hour and when I did I told him not to call the midwives or my doulas becuase I didn't want to wake them since I still had plenty of time. He ignored me and called anyway and we headed out. I was only at the bc for 40 minutes before she was born. I actually was pretty comfortable most of the ride there, still not sure if this was "it" but as I was listening to the tapes telling me to picture my cervix opening up more and more, I found myself thinking "but not too much yet. Open up a little more but not fully yet." I didn't even realize I was thinking that until after she was born and I remembered that and I wondered if I knew subconsciously that I was close and just couldn't let myself fully relax or I would have the baby in the car!
So, my point is (as long and rambling as it was!), I can totally see how a hypnobabies birth can be a surprise. I am planning next time to call my midwife as soon as I wake up with any kind of contractions, even if I'm completely comfortable!