Guess I'll start by saying some illnesses can be very obvious, even mental ones. Professionals use a rubric that was created and edited by other professionals to determine illnesses in patients. Technically that same rubric could be reused by a normal person to determine whether or not they experience something. There are obvious flaws with doing this.. the lack of training and experience for one, and being the person affected could also cause judgement on a problem to be skewed.
However, the only differences I have
really noticed with legitimate diagnosis and self-diagnosis are that professionals usually ask rehashed questions about their patient, and some can provide treatment. Professionals have and do misdiagnose for basically the same reasons any normal person would: mixing up symptoms with another illness, misunderstanding, and even ignorance. I was misdiagnosed and mistreated at
least 5 times by professionals throughout childhood before I pin-pointed the problems myself with research as an adult. Mental illnesses are especially complicated because they stem from innumerable sources and most don't even have a clear-cut definition of experiences since all affected individuals vary. Health professionals also tend to be
able-minded and rarely have personal experience with mental illness. A person from the outside can only judge as much as you'll tell them.. and even a professional won't know everything you deal with just by listening and reading.
With that said I am on the fence about self-diagnosis. I think it's very helpful to understanding yourself and why some things happen-- especially if you have decent medical knowledge.. heck, it can even help you meet people who understand you. But I am aware that it can also be really harmful, because if you're not armed with understanding on what you're dealing with you could misdiagnose and wrongly inform others about mental illness. For example there's an uncountable amount of people who have very negatively impacted a couple mental illnesses that I deal with by spreading wrong information about them and claiming to experience them when they actually don't. Almost daily I run across a joke or statement about my illnesses that was formed out of ignorance, inexperience, and people incorrectly self-diagnosing.
Only for minor stuff, however for serious things such as mental illnesses and what not I do not like that at all. I severely dislike it. I strongly recommend you do not self diagnose mental illnesses. I guess I don't like it because I'd rather people go get help and get diagnosed by professionals instead of self diagnosing and sitting in wallow and pity.
It's been said but I might as well address to you that not everybody can afford to see an expert, much less the treatment they provide. Medical care is extremely expensive and even insurance can be really difficult to get a hold of when you don't have money. Insurance usually doesn't cover the full cost of visits either so you'll still end up paying money out of pocket that a lot of people don't have. If you have the ability to see someone, absolutely do so before self-diagnosing.. but please keep in mind that is a
luxury.