I had a two hour labor with DD (second birth). I had seen a chiro and accupunturist and was good to go... Not expected after my first birth. In retrospect, I felt like I was in transition about 15 min. I sent DH and DS to the park and they walked in about ten minutes before birth. DH immediately called 911 but we still didn't realize how close I was.
I ended up giving birth by myself, alone, in the back bathroom. I was really lucky because I had a normal, fast birth with no issues. Paramedics arrived about ten minutes after birth and cut the cord, transported me to the hospital I'd planned on giving birth at with midwives. Didn't see midwives until hours after birth and mostly got the cold shoulder from the emergency room/OB for what the suspected was a planned unassisted birth. Placenta delivered at hospital.
Luckily, I didn't panic at all when I realized it was happening, didn't even call DH. I was deep into hypnobabies focus and just thought it will be over soon and pushed twice. Pushing was a snap. And I remembered that very fast births are either as a result of a serious issue with the fetus "Hey I need to get out" or very, very normal.
So... I would assume there is a small chance something similar could happen with a fast birth and maybe read up a bit on home delivery if it comes to that. And yes, 911 is a good choice if you need and want to get to the hospital fast. The paramedics were delighted to use their "birth kit."
If we have another I will likely choose a home birth with a midwife but not unassisted, ever, by choice. My plan would be to again, call 911 if things got crazy, have them cut the cord, and transport to hospital, with happy baby nursing on the way.