Hi Robert
It’s highly possible that you’re ‘efforting’ too much! (if indeed there’s such a word).
This issue often happens with people who do not yet know how to optimise their breathing. I KNOW that is sounds crazy that one would not know how to breathe as an adult. This is probably the reason for the nausea.
Go and check out the free video Effective Breathing In Hot Yoga.
The breathing will help you with the energy expenditure and you’ll be able to tune much more easily into your body. Breathing, Alignment and then Depth. They are what you want to focus on, in order.
Keep us updated.
Namaste
Gabrielle 🙂