Originally Posted by Niceguy
it's not age so much because I work at staying fit but it is a factor
but more it's the illness
Should I tell the instructor I have an illness and have to pace?
I'd tell the instructor, but I'd also consult with a doctor. Obviously the only way to improve will be to push yourself, so know what the limits/symptoms are before you start. For example it'd be OK for a healthy person to continue when they're out of breath, but an asthmatic person might need to take that as sign to stop before they trigger an attack.