I have symptoms of a mental health disorder not registered in the DSM-5 called 'maladaptive daydreaming disorder'. In order for this to be able to get into the DSM-5, more research needs to be done on it, by more researchers. I want to do research on maladaptive daydreaming disorder, but I'm not sure if I am allowed to considering that I personally experience it. Would my research be considered biased, and therefore not be considered accurate?
Whether or not a disease is listed in some manual is irrelevant for whether or not one can or should do research about it. For example, COVID-19 wasn't listed in any general medicine equivalent of the DSM (specifically, the International Classification of Diseases or ICD) -- because it was a new disease --, but it is a disease alright and research on it is both welcome and has proven to be quite useful.
Similarly, whether or not a disease is listed in a manual does not affect the ethical guidelines that govern what research is permissible and if it is, how it has to be conducted.
That leaves the question of whether someone who has a disease is well positioned to do research on it. That fundamentally comes down to whether the person believes that they can be impartial about what they find. Not everything you will find will please you, for example: medications or other treatment plans you are investigating may fail to have an effect, or may actually be detrimental. Or it may turn out to be difficult to obtain sufficient statistical information about whether something works. In such cases, it may be difficult to separate your wishes and desires from what the data tell you.
The methodological processes in scientific fields exist precisely to give researchers an objective method they can follow to answer questions, without contaminating the research with personal bias. Presumably, the kinds of psychological research leading to listings in the DSM involves some objective scientific work based on systematic empirical observation of patients or other members of the public, and it ought to be possible to do this research even if you personally suffer from a mental disorder or have some source of bias on the topic.
Psychology is a discipline that has had some difficulties with methodological rigour and practice over the years, and there are various subfields (particularly social psychology) where there is a general view that methodological processes have been poor and substantial amounts of research bias has crept into the field. If you are interested in this, I recommend reading some papers looking at methodological issues in psychology (e.g., Jussim et al 2016, Jussim et al 2019, Clark et al 2021).
In any case, there is certainly no rule that would make your condition a disqualifying condition for being allowed to conduct research on this topic. As to whether there will be a perception of bias, that will largely depend on the quality of your methods and the degree to which your conclusions are supported by objective analysis. The mere fact that you suffer from the condition you want to study would not strike me as a disqualifying condition. Indeed, I would be highly surprised if there are not already many examples of previous psychological research undertaken by practitioners who suffer from the conditions they are researching.
(As an aside, there is a long-standing speculative theory that the discipline of psychology tends to attract students who have mental problems or disorders; it is one of the major stereotypes of psychology majors. I'm not sure if it's true, but if it does have an empirical basis then your situation might not be very unusual.)
You can do research on anything you like, for any reason.
That your own acknowledged experience motivates you will not surprise anyone.
A web search for your topic produces many links to what seem to be respectable sources, so any useful contribution you can make will probably be recognized by that community.
There is no problem in researching something that isn’t in the DSM, other than possible funding issues.
Researching a disease that you suffer from might create a conflict of interest — that doesn’t mean you can’t do the research, it just means you need to report the conflict so that others can give your research extra scrutiny.
Research shouldn’t be rejected because it’s biased, but rather because the methodology is flawed or fraudulent. All research is biased in some way or another, bias is inescapable, science is in part about making bias irrelevant, by making the results repeatable and/or explicable.