can't sleep

Do you ever have those times when you wake up at 3 am and you're just awake? I hate that. Although I would generally speaking rather be awake than asleep, because life is such an amazing rich cavalcade of thoughts and feelings. The reason I hate it is that I know I will 'pay for it' later. Probably at about 3 pm, when I feel sick with weariness (I nearly wrote 'exhaustion', but that would be an inaccurate term; exhaustion is when you've done something strenuous other than just sit/stand upright).