I'm sorry Gym..We're suffering a bit

I've been having some issues with sleep and working out lately. I want to work out, but then again sleep takes over sometimes. it all started around the time my schedule became a bit busier at school. We lost a part time foreigner teacher and instead of hiring a new teacher, they decided to spread his classes around to the rest of us. Well. The schedule is a little rough. Not everyday, but I can feel it taking a toll on me. I want to go home and sleep a lot more. I have less time before the gym just to relax. There has been almost one day a week where I have just fallen asleep and not woke before I make aerobics class. I feel guilty quite often for skipping out, but I almost always realize I must have needed it.
The other issue is I think I was overdoing myself. I was doing aerobics 4 or 5 days a week. running for 3 days and latin dance class one day a week. When I would run.. I would run 10 km ( a little over 6 miles) right after doing aerobics. My knees have been acting up more lately and I just think all of this added to my exhaustion.
So I decided to back down. But the problem is, I'm having trouble backing down. I'm scared of becoming fat. I'm scared of changing my routine. I'm scared of any bad consequences of backing down. But I need to do it. So, I've been working on it slowly. I stopped running so much at one time. I've also started cycling as an alternative. But I still haven't found a perfect workout. I need to find something I can do and something which would enable to change up intensities and also make me feel accomplished after the gym. I'm on the search.
For next week, there will probably be no gym as I will be in Hong Kong. Definitely excited. :)