You only think of yourself as weak, because you compare yourself to people working 12-15 hours every day for years, because they want to "make it" in the software world. In the end, most of them are going to be burned out and depressed, with no family or friends around, because they simply didn't have any time developing that part of their lives. Hopefully, some of them will continue on to do that then later in life.
I'm okay with 7 hours of sleep every day and can function well for 8 hours of work in the work week. But then I need time on the weekends with my friends and with myself to recover. When I'm doing a lot of overtime, the first thing I do on Friday evening is come home, get out of my shoes and fall onto my bed. It's completely normal to be tired after 8 hours of work and needing sleep. Our super-fast, ever changing society puts a lot of pressure on us, and at some point, people will not function under that pressure anymore. Which is why mental health issues are on a high rise.
You may just be getting older. These started for me at 40. And it's not just the physical symptoms: the multiple days of depression and low motivation after they've subsided are deeply unpleasant as well. Drinking to excess just isn't worth it any more, if it ever was.