We've all experienced a sleepless night or two, and for some people that's actually the norm. But why do we experience insomnia at all? What is going on in our minds and bodies, to cause this awful condition? Here's what scientists know so far.

Exactly how long we're supposed to sleep each night can vary depending on who you talk to, but we all seem to agree on one thing: you want to get one long, uninterrupted sleep. But it wasn't always that way.

We already know that not getting enough sleep can be bad for you. And now there's another reason to worry if you're getting sleep-deprived: People who have trouble sleeping may be at higher risk for developing Alzheimer's Disease later on.

Stress, deadlines, or caffeine can give people a few sleepless nights, but there are some people for whom insomnia is chronic, complete, and fatal. Find out about a rare, but scary, condition known as fatal familial insomnia.