Why am I never cold or tired?

I swim open water usually once a week for ~20-40 min usually with a mix of breast stroke and freestyle. Decided today I wanted to push myself and did 1.2 miles in 1hr1min, 59.5F water temp, no wetsuit, pretty choppy (out and back route), crawl stroke the entire time.

So I was in the water for an hour and swam 1.2 miles but did not feel tired or cold. I felt like I could have easily kept going much longer but got out more because mentally I was the only person out there at the end and didn’t want to push it with nobody else around. But now I find myself wondering - could I have done 1.5h? 2h? Where is my limit? Curious if other folks have felt invincible in this way (in terms of not really getting tired or cold). It feels like a superpower of sorts - I always say I was a seal in a past life.