Yes. I just get a strong urge to breathe. But I'm very conservative- I don't let it get too strong.
Maybe I should confess that I probably don't belong in this conversation. I'm not really a freediver- I'm just an 83 year old has been spear fisherman trying to get one more season. I've never done any line diving. I've never done any tables or fancy breathing exercises- empty lung full lung etc. In the kelp beds of California with poor vis its very difficult to follow the buddy system so I seldom have anyone watching me unless I have a fish wrapped up in the kelp on the bottom. Then we try to get our buddies to come back us up but they usually can't see us from the surface. So I really don't try very hard to extend breath hold. Maybe if I were in a controlled situation line diving where the entire point of the diver was maximizing breath hold then I'd finally feel a contraction, but I still doubt it. I've been diving since about 1952. When I was a teenager no one had heard of shallow water blackout and I thought it was perfectly normal to be dizzy and see stars when I surfaced. Its a miracle that I survived, but if I could feel contractions, I think I would have then. But OTOH, maybe I did but just don't remember. Anyway, I'm quite sure I haven't felt any in the last 20 years since I've known that I shouldn't see stars when I surface.