Trip to Nepal and Tibet, Fall 2017

I am planning a trip to Nepal and Tibet for this fall, 2017. I made this trip in 2014. I'm 63 now, but will be 64 by the time I leave. I'm looking at the fitness workouts here, just signed on for the beginner level. On my last trip, we didn't really do much trekking, only a 3 mile trek up to Everest Base Camp on the Tibetan side. It wasn't difficult except for the final 100 meters or so, which was very steep and icy. Most of the rest of our trekking involved climbing thousands of stairs at monasteries, temples, shrines, caves, etc. We joked about how Buddhism was a very steep religion! This time around we will be spending a bit more time in Nepal and doing a one or 2 day trek in the Anapurna region, in addition to all the stair climbing in Tibet. I don't think it will be all that much of a challenge in terms of altitude gain on the trek itself (we have asked our agent to give us something for old, out-of-shape folks -- LOL), but anything at altitude is challenging for those of us who live at sea level (Texas). We will be taking time to acclimatize, so no worries there. I was panicked about being in shape on our first trip because I was fearful of dying on a mountain somewhere in Tibet! Well, I don't have that fear as motivation this time around. Maybe I should, but I don't. I'm finding it difficult to get motivated to shift my diet and really get into workout mode. I have never liked getting hot and sweaty, especially now that hot flashes and night sweats seem to be worse when I do. I need some other motivation. This is all a mind game for me, it's clear. Any suggestions on how to shift my attitude would be greatly appreciated!