Another guy who just made an account to reply to this, and yes I know its old as hell. I'm 35, been smoking since I was 17, I also study mental disorders psychology, and have a degree from a very well known school to prove it.
I'll try to make this short and to the point for anyone who is interested or worried about this particular disorder called derealization. I've actually always referred to this before I learned about it, as living in the Dream State, or in the Cloud.
I've also dealt with this more than once in my life, so I know what I am talking about.
I don't want to scare anyone, but this derealization you are feeling is actually brought on by more than just smoking weed, no matter how much you smoked or how high you got. Marijuana is like dealing with your best girl but one that's finicky and a pain in the ass.
First, for the guys who are wondering if something bad will happen if they smoke, smoking is opposite of drinking. With liquor, you take some shots and feel it hit you 20 to 30 minutes later. With weed, anyone can take a hit or two, hold it in for a few seconds, and chill for a few minutes. You will know right away if you are liking it or if things are going badly. If 10 minutes pass and you're totally fine, you can always go back and take another hit or two. Don't be the guy who smokes the whole joint or blunt to the end on your first time smoking after a while or ever before, you will probably regret it.
That said, on to the disorder of Derealization.
The weed we smoke today, is very different than the stuff our parents smoked at woodstock. This stuff is very potent. As a matter of fact, go give an older guy that you know who smokes or used to smoke a lot, a hit of some bud you have. Chances are he probably gets the same old bud from his buddies that he's been getting for like 30 years, and probably decent stuff but what you or I would laugh at. I guarantee a few hits of the newer bud around will put that dude on his ass, and he will probably go into this dream state just from the huge spike in mental depth he gets from the stronger bud.
Now, back to you and the good and bad news. Yes, weed will help a LOT to spark this state of mind or lack there of. Weed, like any drug, and again we are talking the potent stuff that we smoke nowadays, WILL alter the mind, and put you in a different state of mind. That is natural, that is why most people choose to smoke it as an escape from something.
Sometimes, this can last a long time, sometimes not. Here is where it gets confusing. There are currently no real known "facts" about this "disorder" and probably won't be any time soon. Why? Because the factors are completely different for everyone, and every time you encounter this it can hit you different. What works this time to get you out of it, might not be the cure if it happens again.
So, to try to summarize my thoughts best I can, weed will every so often, put many people in this state of mind. It happens every so often with a lot of people, and many times it is recurring later again in life. Funny thing is, some people that never smoked weed still get this "disorder."
I put quotes around the word disorder, because its important to know that it's not a disorder. Its a state of mind. But, its deeper than your regular mental expressions in many ways. And, yes, it does usually feel like you are disconnected from yourself and can feel like looking through a window at yourself.
But, the good news, is that it will go away. When? I don't know. Could be few more days, could be weeks or even months. Fortunately, this is not LSD, its very strong strains of marijana. Can you smoke yourself stupid? Yes you can! But just like this "disorder," with time it will eventually go away. You may even feel this go away even if you don't stop smoking.
But if you are really worried, and its affecting your life in some ways, for sure the best thing is to probably take a break from smoking, and I don't mean a few days.
I find with myself and others that i've talked with about this, in most cases when this state of mind hits you, its pretty staggering, and usually needs at least a good two or even three months for the brain to get rid of this cloud, and things begin to clear up and feel normal again. Again, this is most cases but its always different.
So, if its been days or weeks and you still have this mental dream state thing going on, thats fine because its natural. If its severe, which it usually is after something has been bottling up inside and comes out with a spark like smoking some extra strong weed, more than usual amount, getting high after a long time without smoking, etc. etc., than it is going to take the two solid months or even a little more depending on the person. Yes, some people might go back to normal without quitting and no real explanation, same as how they got here to the mental state in the first place, that happens too.
My advice to anyone reading this is to relax, and know that it's temporary, and always is, unless you do other drugs or go through a real screwed up situation in life or something extreme like almost dying, etc.
It will go away, but will probably take more time than you thought, just stick it out.
Its actually a good thing, if you smoke a lot of weed, to take some breaks here and there. The human mind does not do well with anything thats being used every single day, unless its water.
So relax, you didn't fry your brain by smoking too much marijuana, or spark some sort of permanent personality disorder. Weed will make you feel like that, especially if you are talking prolonged use. Weed will also make you feel like you have OTHER personality disorders too, so be careful.
Even guys who have smoked every day for 30 years and became close to a vegetable

, can go back to almost 100% normal and mentally sharp again, with quitting or stopping smoking weed, but since that case is so extreme, in those cases it takes usually more than a year or close to it at least.
And yea, memory, appetite, clarity, focus, self identity.......all of it. It all gets screwed up when you smoke a lot of cannabis, and will eventually go back to normal with enough time.
Marijuana is great for a lot of things, but like most things in life, it has it's negative things too. Find a balance. Take breaks here and there. IF you are dealing with this dream state right now, than just stop smoking for a few months, its only going to help. It won't hurt you, thats for sure.
Trust me, you're not going to be missing anything, the friends and weed will still be there waiting for you when you get back. In fact, they always will be. But smoking this strong bud we have everywhere now, like on an every day basis, will surely screw up your mental health, physical health, and probably your life. So don't abuse it. Use it as its intended, like a tool.
Hope that helps someone that may read this. I've studied this, along with other mental disorders in great detail, and I speak from personal experience also.