Disorders? What disorders are you talking about? You know the ones that people are always focusing on. Multiple personalities, schizophrenia, attention deficiet disorder, depression, etc. What would a 19 year old know about those? Well as much as experience can tell me.
I was diagnosed with attention deficiet disorder in grade 3, and it has never gone away. I still struggle with concentration and focus even today. That's why Huri|Net is so unorganized and chaoticly arranged. Depression? Well that one has never effected me up until last year. I have always been positive and uplifting but some time last year something snapped and now every once in a while I will get into a really really depressed mood which scares me because I don't understand it yet. As for multiple personalities well I think there are several types of multiple personalities that people focus on. The most common misconception is that schizophrenics have multiple personalities. This is not always true. Yes a scitzofrenic may have multiple personalities but so can a person who is not inflicted with any other mental disorders (I hate that word, disorder, so from now on I will say differences.) I have known several scitzofrenics and so far only one of them had multiple personalities, but I have known far more people who have various forms of multiple personalities than I have schizophrenics.
Multiple Personalities. Now what do you mean by that word? Well there are several meaning to that word in my mental dictionary. One is that the person has actually developed other personalities that struggle with each other for control of the person's mind. Another is that they have created alternate personalities are actually all the same person but with different personality attributes. A third is not actually a personality but a completly seperate being that has entered the mind of the person and is effectivly possessing that person. This may not be bad if the person summoned a good or neutral being for assistance but if an evil being has taken over the mind of a person it is called demonic possession and it is a very dangerous and serious matter. Sometimes beings like to enter through the spirit to get to the mind. This makes them much harder to get rid of because although you can clean out the person's mind the being is still within their spirit waiting for another chance to attack the person while they are vunerable. Various religions have methods of casting out evil beings from both the mind and spirit and this is often called exorsism.
The majority of multiple personalities will not be external beings, and the majority of external beings that enter people are not demonic creatures, however this does not mean that such things do not exist. There are demonic creatures and they are very dangerous. If you notice someone acting quite strange, like a totally different person in fact, and the change is for the negative, you may be witnessing the effects of a demonic influence (and no, women effected by PMS do not count as being demonically influenced.)
Now using external beings for the assistance of the summoner has been a practice of many beliefs for centuries. Others have done it without even knowing it. As long as the being is there by your own will and will leave when you ask, you are not demonically possessed.
Alternate personalities are quite interesting and are a normal part of life for many people. Alternate personalities unlike external beings or multiple personalities are all the same person, however they have different personality attributes. For instance one person could have their dominant personality being a kind hearted icon of innocence, but an alternate personality of that person may be a sadistic party animal. To distinguish between the two personalities the person may actually give a name to the other them. Now usually a person won't just have an alter-ego but an entire collection of alternate personalities each with their own unique attributes. This is not to be confused with multiple personalities who each are different people within one mind. Multiple personalities unlike alternate personalities will not share the same memories, and these are the personalities that are usually focused upon by those who talk about muliple personality syndrome (or disorder).