Stack Exchange in general discourages questions that are "too localized", meaning that they only likely apply to a small set of people, and will not be very useful to future visitors looking for material on that particular topic. Since everyone is quite different, it's difficult, if not impossible, to generalize advice, and even if we could, we shouldn't.
Can't we just try our best and dispense what we think will work? Well, why shouldn't we, this is the internet and people come to Google first for help all of the time, right? Certainly, I can fix my own brake hydraulics in my car using instructions from Joe's Auto-matic.com (sorry Joe), but I'd hate to put my own safety at risk by not taking the advice and harnessing the experience of a professional who deals with this type of thing all of the time, and is certified to do so.
Likewise, in cases where you are seeking help, you should seek advice from a doctor or licensed mental health professional who can see you in person, learn the important parts of your history (medical, social, and psychological, without you having to share it with the interwebs), and can tailor a treatment or other plan that is right for you. How can we tell if your "brief funk" isn't due to an autoimmune disease, and someone telling you "just smile your way out of it and read Aaron Beck's books at bedtime" isn't going to put you in danger? We're thinking of your own safety here, and not in a patronizing way, but in an "it's your own safety" kind of way!
But, you ask, what if the person answering the question is a licensed doctor, psychologist, therapist, or nurse practitioner? Well, laws vary in terms of right to practice under certain conditions, and any quality clinician should want to see you in person, at least once. I think you would find that most responsible clinicians, even if they could treat over the internet, wouldn't risk their license to provide you with sub-optimal care anyway.
But, you ask, what if the question is not really a self-help question - it is a question about someone else, or about a group of people? Well, keep in mind that while you may not be concerned with your own safety when asking questions about others, a concern for safety remains for other readers of the post. To form a diagnosis, a mental health practitioner typically consults a checklist of possible symptoms. In asking a question about an individual, you may not include all the needed information, and when asking about someone else, may not even have access to it. At the end of the day, this is a Q&A forum, and is simply not designed for the interaction necessary for a valid diagnosis.
The good news is, any questions regarding conditions in general are fine. Feel free to ask about the prognosis for a certain condition, the biopsychosocial basis of it, pointed questions about current research, but just keep it to questions that will be useful to someone else in the future, and in general, have some scientific or clinical basis. Someone else in your shoes who searches for information on it in the future will thank you.
Remember that closed questions can be re-opened if they are edited and improved. You can edit your self-help question and change its form so as to remove anything personal in nature and frame the question scientifically, asking about the causes, prognosis, the biopsychosocial basis, or specific details about current research. Then, respond to some of the comments asking for feedback/reopen votes, or use the "flag" link to request moderator feedback.