You can start with Harvard Medical School Guide To A Good Night's Sleep.

Well, sleep debt is something that is accepted by the majority of sleep scientists, so although I can't explain you the processes behind it since I'm not an expert, I'm sure you can look it up.

The reasons why people say that they feel worse when they "oversleep" is usually:

a) They are sleep deprived. If you have accumulated a lot of sleep debt, you won't erase it by sleeping for 12 hours once, therefore surprise surprise, you will still wake up sleep deprived. I'm not sure if that's correct, but I understand that it works in the same way as being starved, if you weren't getting nutrients for an extended period of time, once nice lunch won't solve the problem. 

b) They wake up in a time when temperature drop is happening. There's a temperature drop that happens that usually happens in the afternoon (it obviously varies on your sleep cycles though). Therefore, if you usually wake up at 8am, and one day you wake up at 12pm, that means that in few hours there will be this drop that will make you sleepy. 

I suggest you to read up on sleep, there are plenty good books on the topic, plus loads and load of scientific papers as well.

That's a very good point.

I think most people don't understand how sleep debt works (or don't even realize that such thing exists).

It's very likely that a person who sleeps ridiculous amount of time if they don't put an alarm clock on has accumulated a massive amount of sleep debt over the years.

Scientists who study sleep seem to have different opinions on the issue of oversleeping.

Some say that it's impossible to sleep more than you need because   of physiological processes meaning that once your body is fully rested you will wake up and won't be able to fall back asleep.

You see, if you never used to drink, and your friends know that, that's one thing. 

However, if you used to drink a lot with your friends, and suddenly you decide to stop, then that's a completely different story.

I have seen quite a few friends who decided to stop drinking or smoking getting rejected by their former party buddies. 

I think that's because if two people always party hard with alcohol/cigarettes/drugs, and suddenly one of them decides to lead a healthier lifestyle, the other one often feels guilty.

I'm actually surprised to see so many people who don't drink alcohol.

I spent my teenage years in an environment where people don't drink/smoke/do drugs (martial arts) therefore I never go into any of that and neither did most of my friends from that time. 

I have met very few people outside that martial arts community who have a similar attitude, though.

I think it's not so much about trying to repress feelings or sexual attraction towards someone as it is about consciously choosing not to act on them. 

We have  limited willpower and cognitive abilities.

It's not smart to waste them on trivial matters such as "Should I watch another episode of Breaking Bad?" or "What should I eat for breakfast today?".

Contrary to popular opinion, resisting a lot of small temptations and making a lot of small decisions doesn't result in an increased willpower and cognitive abilities, it results in the exact opposite of it: ego depletion, at least in the short term. 

I think this principle applies to relationships as well.

In our society, we put a massive emphasis on romantic love and sexual attractions, and tend to think that if we "like" someone then we should totally try to move things further.

In my opinion, that's a mistake, since this way people often get into relationships that can't possibly work out well. I think it's much smarter to ignore that "I like him/her" feeling if that person is clearly a trouble. E.g. It's probably easier to not start to date someone who is an alcoholic than to get out of an existing relationship with an alcoholic.  I think we could all avoid  a lot of trouble and heartache by bringing a bit of rationality into our love lives. 

I have a very similar attitude to this "first temptation" issue.

I actually learned it with watching TV shows. I really enjoy watching them, but I know that if I watch the first episode of a good show it will lead to watching all the seasons of that show in a short period of time. That's why now, that I came to terms with my apparent lack of willpower I avoid watching anything new. TV shows are not a really dangerous temptation  though, because you once you watch all the seasons, you are done (that's why I schedule my TV show binges, so I could watch all the seasons of some show in a short period of time guilt-free, and then move on with my work)..  Ever-present temptations like alcohol, cigarettes, drugs, computer games, social networking, are way more dangerous. I remember I was thinking few weeks ago about this exact same topic and how easily people could avoid many problems in life (alcoholism, drug addiction, etc.) if only they would refuse to get on the slippery slope. Everyone thinks that they have self-control, but what they miss is that there are no alcoholics or drug addicts who said "I know I'll become an addict" - everyone thought that a drink here or a few joints of weed were nothing to be worried about.