there are things in this world that cannot be explained

Yet. Just because they are unexplained now doesn't mean that there isn't a logical explanation. Remember, people once thought the sun revolved around the world and that the world itself was flat.

to questions somebody's mental stability for perceiving in something that we don't understand is rather rude. Unless you have some serious letters behind your name and the prefix Dr. in the front, nobody really has the right to make those statements about anybody's psyche.

Questioning and ruling out logical possibilities isn't "rude." Unless someone is trying to diagnose OP as a schizophrenic I think you're being overly-sensitive. If someone did suffer from a mental disorder and claimed a ghost was haunting them then logically that is the cause of their "haunting." They may not even realize it because it seems so real to them. It's always good to have an objective party present to help you account for things you may have missed. You don't have to be a Doctor to know the symptoms of a condition when you hear them. Suggesting that it could be a possibility isn't the same as diagnosing it.

Moreover, it's been proved that if somebody who is classified as sane is injected into a mental institution, there is little to no difference between the sane patient and those that are considered mentally unstable.

Explain what you mean by the lack of distinction between sane and unstable. I'd like to see this "proven" research you're referencing to.

There are also thousands of shamans (and please be polite when stating your rebuttal against this point) who for centuries believe that those who have schizophrenia are actually souls that are evolving into a higher realm of consciousness.

Offense is taken not given, so whether or not you get offended by what I say is on you. I am merely presenting the facts as they stand. My goal isn't to offend but to educate. Now, indigenous societies also had other beliefs such as the sun being a God that needed to be appeased by throwing children in volcanoes. They had little to no concept of how the world truly worked only on what they perceived to be true. Citing them as a reference doesn't help your cause. This has absolutely nothing to do with what we are discussing.

Now I have no proof to say that this is fact, I just think that we as a collective shouldn't immediately scream medicate and sedate to anything we don't understand.

I have yet to see anyone say that people who post their experiences here should medicate or sedate themselves. I'm not saying it doesn't happen, but if it did I'd consider them just as naive as people posting they saw a shadow and thought it was proof that ghosts exists. What I am advocating is the use of critical thinking and logic to come to an educated conclusion of what could possibly be going on. However, going around and saying "nope, that's not it, it's ghosts and demons. There's no other possible explanation" when educated hypothesis have been given is ignorant. Nothing gets accomplished. We must have an open mind to the unknown, but we must also have an open mind to those offering suggestions.