I have been having a lot of trouble on SO lately because I suffer from an array of mental health conditions. I am open about my conditions and don't mind telling people. But I can imagine the backlash of stating in a question that "please be nice because my anxiety might cause me to have a breakdown". I suffer from such extreme anxiety at times that my head just cannot cope but people are quite unkind at times on SO! I also have problems being polite to people who are not so polite to me and can sometimes end up embarrassed by what I say in haste, due to personality disorders. I recently had an issue with a high rep SO user seemingly playing strange games of commenting strange and rude comments and then deleting them. I tried emailing SO for help but was given a generic reply and just ignored by my further attempts to see what I could do. Obviously I couldn't flag comments that had been deleted. What is the best course of action to stop people from causing my head to go in a complete spin by being not-so-nice. N.B please be nice :)
First of all, I can understand your frustration. I suffer from a similar (albeit less intensive) situation (mild anxiety and ASD).
The problem with your approach is that the Stack Exchange format is just not designed to take the user into account.
In contrast to a traditional Q/A or forum-style format, Stack Exchange aims to first create a library of high-quality questions and answers with as little noise, discussion, or pleasantries as possible obfuscating them. This has worked well over the years, but it also means that the feeling, experience and, yes, treatment of the asker is secondary to the usefulness of the Q/A to future visitors. This means that Stack Exchange treats every post as standing on its own, ideally without considering the author whatsoever.
All community moderation is geared this way. You don't see context of what a user posted in review, you're not supposed to consider who posted what when voting, downvotes are anonymous and at the discretion of the users casting them, unless (and that's the only unless) you target them at a specific user. Yes, that means that I can go around downvoting everything I see when I have a bad day, but going through and downvoting a specific user's posts in a serial way is a punishable offense.
Following from that is that the Q/A format here fundamentally does not permit exceptions or special considerations based on author status. That is a rough thing to grok - I can understand, downvotes and negative feedback can quickly feel personal (especially to someone with anxiety).
I also have problems being polite to people who are not so polite to me and can sometimes end up embarrassed by what I say in haste, due to personality disorders. I recently had an issue with a high rep SO user seemingly playing strange games of commenting strange and rude comments and then deleting them. I tried emailing SO for help but was given a generic reply and just ignored by my further attempts to see what I could do. Obviously I couldn't flag comments that had been deleted. What is the best course of action to stop people from causing my head to go in a complete spin by being not-so-nice.
I don't think you have any course of action here except trying to deal with the problem better on your end. Particularly
Commenting for people to take your condition into consideration is likely to be unfruitful, such comments are frequently removed as no longer needed or obsolete. Comments are only supposed to be used for clarification or direct actionable feedback or direct criticism on a post. Even those are regularly deleted after their purpose has been served. In addition to this you are likely to invoke a form of Streisand effect (requesting that people do not downvote or close vote causes people to do it more, in any form).
Editing such a passage into your post would likely be removed as noise (posts are supposed to contain only material directly related to the question or an answer thereof). It also triggers the same Streisand effect.
As you have noted, Stack Exchange staff is not really able to assist you when contacted about something like this, as its a function of their Q/A system and changing it to suit these purposes is currently unfeasible and undesired by the community.
Moderators can not do anything beyond deleting actual rudeness, for which there are dedicated flag types.
What you can do
Actual unfriendliness and unkindness or verbal abuse is against the Code of Conduct. This means that it is actionable by moderators. You can flag comments containing such as unkind or abusive, and if they are found to be by moderators, the comments will be deleted and if the user has a history of doing something like this, they'll be sanctioned.
Please note that even though something can feel like an attack, it's possible that it's just criticism. In that case moderators will not remove it or sanction the poster. I fall into this trap from time to time and have to remind myself to not take things personally. It's really important on here.
I guess we have the service dog problem. Proper service animals are well trained, often unflappable professionals. Some folks though stick a vest on their pet to get them places they won't be allowed. The problem with a 'handle with care' message is I am doubtful it will have the intended effect.
I've suffered from anxiety in the past. It's not great. And I found it's very hard for people to actually realize you are in an anxiety attack even when right next to you and are family.
And therein runs the hard problem. We can't really make excessive allowances for your behavior. Folks would often use it as a way to get around our norms. If you're clearly having other sorts of trouble people often help.
As for other folks, if you're seeing a pattern of unkind comments from a user and they are constantly doing it, try flagging the post the comments are attached to explaining what's happening. Screenshot it if you can (but mods can see it anyway). We want people to focus on the posts and there's no room for folks being unkind.
I think there's a big difference between someone saying or implying that you are not clever (as an example) from someone saying the question/answer does not meet certain standards.
It is difficult to tell if the OP has cause to complain without knowing what these strange or rude comments were. Even harder if the user (or bully) deletes their comments within five minutes (I think comments that are deleted within 5 minute are non-traceable but I could be mistaken).
Next time, take screenshots of these comments, it would be better if they occurr over a period of time, and always flag them. One important piece of advice I can give is to not interact with this person. Ever. Then, if the flags result in no action, calmly inform the user you now have a record of his/her behaviour. That might stop the harrassment, if it is harrassment. If the user continues to post and delete insensitive or hurtful comments, I strongly suggest that you contact SE via the link at the bottom of the page and describe in detail the comments, and if possible, include those all-important screenshots.