If you still feel tired after a good night's sleep, you're probably dehydrated. Drink some water after you wake up.

— Just So You Know (@Know) April 22, 2013

Some quick searching unsurprisingly indicates dehydration is a potential source of fatigue (see #10), but is there any medical evidence that dehydration causes fatigue despite proper sleep and that drinking water after waking up will improve wakefulness—as the tweet implies?

  • I recommend clearing up some confusion here - "dehydration results in fatigue" is a separate issue than "drinking a glass of water when you wake up makes you feel alert". I recommend narrowing this down. For instance, the drink might make you more temporarily alert, but still not necessarily hydrated, so the question would remain unanswered (and the test of drinking water upon waking is ambiguous). – VCavallo Apr 30 '13 at 21:37
  • 2
    I'd guess the more likely diagnosis is sleep apnea. – Mark Hurd May 4 '13 at 2:57
  • "you're probably dehydrated" is unconditionally true. Humans seem to be the only animals not smart enough to drink enough water. Dehydration does result in fatigue. All improper conditions of the body result in fatigue. – user29285 Apr 20 '16 at 1:43

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