Gary:
The heat has been bad - but hopefully we are now catching a break in the weather so no excuses get out and ride!!
Before when it was hot, I would wait until after 6 pm and then get on my bike. I'm in Orange County and like SD, we catch the afternoon breeze off the ocean. OK at 6 it was still hot and I would work up a sweat but by 7 it started to cool down and by the time I finished I felt great.
I think everyone has a slump and I never fret - I think it's our body's way of saying - maybe you need to take time off. So I take it easy and next time on the bike I feel good, I can usually push a ride. Just don't get down on yourself for not riding, but also don't quit... like I said its nice out right now... hit the road!!!!