While some people attribute insomnia to complex mental problems, a new study has found that some folks can't get a good night's rest because they're afraid of the dark.

Researchers studied a group of college in Toronto and found that almost half of them who said they slept poorly also said they had a fear of the dark.  The researchers confirmed this by measuring the students' blink responses to sudden bursts of noise while they were in both the light and the dark. They found that the students who slept well got used to the noise bursts but the poor sleepers grew "more anticipatory" when it was dark.

These poor guys were so freaked out about things that go bump in the night that messed up their sleep cycles. Taryn Moss, the lead author of the study, explains a little more on this theory (via Science Daily):
As treatment providers, we assume that poor sleepers become tense when the lights go out because they associate the bed with being unable to sleep. Now we're wondering how many people actually have an active and untreated phobia.
So don't feel ashamed about needing to sleep with a nightlight on, especially when your health is on the line.