I also, a couple of weeks back, started having problems with being exceptionally tired all the time. At first I put it down to migraines, because it started the night there was a thunderstorm and I got one, and I got bad sleep because of that, but it went on a while longer than I expected. I started to think it was sleep apnea, because I snore and it's something I've always wondered about, and toyed (again) with the idea of asking my doctor to order a sleep study.
However! The reason I should listen to myself? Because when someone tells me that they're watching what they eat and exercising and are tired and exhausted all the time, I tell them that maybe they're not eating enough. Once Ifinally remembered that, I bumped my calories up to 1850/day from the 1650/day*. It's been about 3 days now and today I am not as exhausted as I had been previously, and I am also not feeling much of the exhaustion effects of the workout from last night, like I had been in previous weeks (mostly feeling sluggish in the muscles that I'd been working on the night before). Major duh! time!
Still vaguely concerned about sleep apnea, because I always, even when not doing anything about eating and exercise, seem to be a quart low on sleep, but at least I think I'm back to my usual baseline. Ah well, time to build muscle.
* Note that these numbers are net, not gross. In other words, if I walk more than usual or work out, I eat more to compensate for that, so my actual intake is usually ~150-200 calories more than the "target". I think aiming for 1200 calories/day, especially while working out and not eating more to compensate like many diet plans tell you to if you're a woman, is in most cases tantamount to starvation.
ETA: I am now very sleepy, but it has more to do with just having eaten lunch (the grilled chicken spud at McAlister's Deli, 'cause I had a free meal coming to me after sending them email complimenting the employees there for always being terribly pleasant), and having walked back to work in near-100°F temperatures. Naptime!
ETA2: Geez, I just checked the weather and tomorrow they're predicting 109°F!!! AUGH
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