insomnia is definitely part of depression. or as my docs would say 'poor sleep hygiene.'
this s.a.d. is not a northern hemisphere problem right now because we are in summer. but there are therapies specific to s.a.d. one of them is purchasing a big ticket item called a 'lightbox.'
you are supposed to sit under this thing a few minutes a day. my headshrinker says it works.
i use a cheaper solution: some lighting stores sell special incandescent light bulbs for about triple the price of a normal bulb. these light bulbs are purple-ish and are called 'full-spectrum' light bulbs. i have one in my bedroom and i read by it year round.
i have to admit that i am a bit of an amateur vampire. no i don't lurk around giving hickies to goth girls but if you know any who are interested i am game. what i mean is that because i am very fair-skinned and red haired that i am naturally supersensitive to the sun. also this sensitivity is aggravated by psychopharmacological agents (wow i spelled that!). so i have a habit of staying up later, going to bed later and taking doses of vitamin d with my evening meds because i don't believe my body is going to normally make enough d as i avoid the sun. keeping a good but not overdosed d level and folic acid level helps me keep depression at bay year round. my sad is much diminished to what it once was. And that is how i do it. my biggest problem from this regimen is that i sleep more than most persons should. but i can't hang that on the fancy light bulb and vitamin d. you can try this and see if it helps you. of course i recommend you also try ingrid/daves idea about exercise although when i am depressed exercise seems to be an impossible solution because the energy isn't there. practically exercise is a good prophylaxis and it helps deal with the weight gain from ssri-s. but once you get depressed exercise is just another nothing-doing corporation.
good luck
pi