Depression. Contrary to popular belief, depression can wreck your life. It's not just a 'phase' people go through. And sadly, most people can't afford the medications they need to fight depression because most insurance (BCBB in particular) refuses to pay for 'useless' drugs.
Also on these boards
quote by Elizabeth Wurtzel - This is the thing about Depression - a human being can survive almost anything as long as she sees the end in sight but depression is so insidious and it compounds daily that it's impossible to ever see the end The fog is like a cage without a key