I'm saving money to buy a massage lounge. Not a fan of psychiatric drugs for mental and sleep disorders. Nobody can be normal. A little imbalance in body chemistry or brain chemistry is nothing to be anxious of. I didn't read ONE book or googled a FEW web pages. I did my research.
Sleeping Disorder

Wow, 12 hours uninterrupted sleep sounds great. I've it sometimes and it quadruple my feel good factor all day after. May be it's something wrong with? Should I ask a doctor? I was told that 8 hours sleep is the best. What about people work on shifts for a years?

Sleeping is the ultimate escape. Only nightmares disturb. While many can't sleep 8 hours because of hyperactive brains, Many can't sleep well because they worry too much. For less worries, play more! Play chess and join forums. P.S. The forums aren't for sensitive people.
People need enough sleep in order for them to do their work correctly. You can encounter a lot of problems when you don't have enough sleep. Thus, we need to consider factors that affect our sleeping pattern. I think melatonin will be a big help when it comes to sleeplessness.
Now that I scroll through the forum, I just noticed that you’ve experienced depression and during that time would sleep up to 12 hours. If you haven’t done it already, you might want to talk to a mental health specialist and figure out if you need to treat your depression. Maybe treating your depression would result in better, consistent sleep. Also if you notice other symptoms of mood instability, I suggest to tell the mental health professional that too.