(wife-jack: Go talk to your doctors. I would at least talk to your GP and your endo about this, since the GP knows you and the endo knows what's going on with your hormones. Plus, fatigue is one of the side effects of synthroid, if that's the thyroid medicine you are on.posted by FlyingMonkey at 5:18 PM on February 7, 2009
Brainwise, "mental clarity" is one of those things that seems really easy to pinpoint but probably has several different neural substrates: I'm not a particularly cognitively-oriented brain geek, but I'd guess the feeling of clarity arises from a combination of activity in prefrontal cortex, amygdala, basal ganglia, and other midbrain/hindbrain regions -- basically, stuff dealing with attention, motivation, and sleep/homeostasis. So in order to really experience mental clarity, you have to a) have the ability and motivation to direct focus to whatever cognitive task is at hand, and b) not be so tired and/or physically wrecked that you can't pay attention.
Exercise is good and has several beneficial effects on the nervous system: in addition to the other effects of exercise that have been enumerated above, exercise increases the level of BDNF (a peptide that protects neurons from death as well as increasing their excitability), and will improve your blood oxygenation levels. So keep exercising even if it doesn't really feel like it's helping your mental state. Especially since thyroid meds can also mess with your heart and bone density, and you want to keep your heart and bones functioning well.
The bad part is that changes to cognitive functioning from exercise/meditation/what have you will probably take several weeks or months to show up. You basically are retraining your body and brain to function properly, and it can't happen overnight -- if you're only giving your mind a week or two of whatever new thing you're throwing at it before giving up, you aren't going to see any improvement and you might actually see a decline, from always changing your routines (this is stressful to your brain and body, and the brain just falls apart under stress).
Also, a lot of medicines that up neurotransmitter levels tend to also have side effects adversely affecting cognitive function. You could try a stimulant, but it might make you more foggy. You could try an antidepressant, but it could make you foggier or actually sleepy, depending on which one you were on. So I would make sure that you've given at least four to six weeks grace period to your exercise/meditation/etc. fixes before giving up on that as an avenue to feeling clearer, and be careful about what medicines you take if you decide to go that route. Just because your GP or endo gives it to you doesn't mean it's necessarily the best choice for you.)
Try upping your protein content and it could up the production of dopamine and norepinephrine which cause alertness.
What's your diet like? Your average lunch? Maybe try to throw an apple into lunch and a protein shake?
/IANAD or anything close I just used to get really tired around 3pm.
posted by zephyr_words at 7:16 PM on February 3, 2009