I also find myself getting tired earlier and earlier in the evening. I hit a certain point at night when I realize I'm finished and have about 2 minutes remaining to brush my teeth before I literally lie down and fall asleep for the night. It's like an aura that hits someone before a seizure. I get this feeling that I'd better be ready to sleep in a few minutes because my energy is gone. It's the same kind of panic and urgency you feel when you see you have a 1% charge remaining on your cell phone.
Another feature of aging is that I am more prone to injuries now and they take longer to heal. I no longer have cool stories to tell about why I am limping but now have to give embarrassing answers like "I hurt myself taking clothes out of the dryer." I also experience odd phantom injuries in my hip and shoulders that come and go. Some days I am fine and others I can hardly walk up stairs.
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I've already experienced many mid-life crises over the years so I'm not sure if I need to find a different name for what I'm feeling. Some days I get a little frustrated or depressed with a body that doesn't perform like it used to but I'm not going to give up. In fact, I have a chip on my shoulder about getting old. Years ago I set a goal to be able to dunk a basketball when I was 50. I'm now 50 and it's been a couple years since I dunked so I guess I need to start working on that goal soon if I'm going to make that happen.
My body may be working slower than it used to, but on the bright side, my nose and ear hair is growing faster than ever before.