For me the biggest difference was the pacing and the freedom.
The Pit labor was like the end of my natural labor - but for 14 hours straight.
I had contractions one right after another with the pit with them lasting about a minute each. But as soon as one was ending the next was beginning. There was no break at all between them. It was exhausting and yet I couldn't rest because I was hooked up to all these machines and I had cranky nurses coming in and yelling at me from time to time.
I felt pain with the Pit, but it's hard to tell exactly what the source of the pain was. I was uncomfortable in the hospital bed, angry at being there and being forced to be there (docs told me they'd drop me from care if I didn't immediately go straight to the hospital from the OB office and begin induction). I had an IV in and external monitor to begin with. After a few hours the OB broke the amniotic sac (without consent or even notice) and attached an internal monitor into my son's scalp (again without consent or even telling us he was doing it). I honestly couldn't have been any more uncomfortable than that!
I had contractions like that at the very end of my DD's natural labor, but I was at home and free to move and act as I wanted to. For me the key difference was that freedom and control over my own movement and actions!

The contractions I had with my natural birth were intense and some took my breath away, but I didn't feel pain - it was different. I felt like I was working really really hard - sort of like you feel after a really hard work-out. You're tired and a bit worn out, but yet energized.
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