Participated in an Olympic distance race to day. After 200 meters on the swim I almost could not breath, felt very strange, even started talking (!) with some other swimmers. After 500 meters I had to take my wet suit off and then things started to go better. The water temperature was around 22 degrees centigrade, perhaps as much as 23. Could over-heating have been the reason?
No ones fault but mine, I should have known not to use it, but it was a little bit scary.
Sure, 23C can make you feel warm. Drink plenty before the race. During IM Switzerland in 03 the water temp was 23.9°C, yet many thought the water was warmer, 24+. I think they cheated to make the race wet suit legal. I’m not stupid and not wear the wetsuit if all other are. It was hot, so I took my swimcap off after 200m. I know the rules say that you have to wear your swimcap, so I started with hit. What can I do if swimmers were fighting so hard that my cap came off? 
It definitely helped.
You suit could be too small.
If the water’s warm, there’s no way I’ll wear a (full) wetsuit. Instead, I just wear the bibjohn from my T1. I get most of the wetsuit advantage (lots of leg buoyancy) and no heat issues.