Some nights I have sleep onset problems that can take well over an hour. I will usually either notice that I have excited thoughts or anxiety/tension while I am lying in bed. In this condition, l have found that doing a sitting meditation is better for clearing my head than continuing to lie down. I try to sleep again after I'm calmed down.

I'm a beginning meditator and can't address MinibearRex's concern about an experienced meditator possibly being too alert. If I was concerned about this, I'd just set a timer to schedule when I'd resume attempting sleep.