For the last few months I've had episodes of extreme tiredness and sleepiness. It cones on suddenly. I feel like I can't hold myself up or keep my eyes open; I just want to drop where I am and sleep. However, even if I lie down, I don't can't fall asleep. It an last 30-45 minutes and as it passes, I yawn uncontrollably. Then I'm perfectly fine again like nothing ever happened. Could this be narcolepsy if I don't actually fall asleep?