I was informed by a moderator that my posts had been flagged more than any other user by a huge margin, both on the main and meta sites. He pointed it out in a private moderator message which says I will be suspended for a month. It seems that he regarded the above fact as one of the reasons for my suspension. Since I have no idea why my posts on the main were flagged so many times, I don't know what to do to avoid the suspension if that is the case.
Note: This answer has undergone a severe edit. Some comments below may now appear to be non sequiturs.
The following is based on my (admittedly limited) experience of being a moderator here on math.SE.
Having many posts flagged would not itself warrant a suspension. Otherwise some rogue group of users could start flagging every post by, say, Brian M. Scott causing him to be suspended. Even having numerous flags on your posts judged to be "helpful" would not itself warrant a suspension. Posts are occasionally flagged to become Community Wiki, for example, which, while helpful, certainly shouldn't cause the owner of the flagged post to be suspended. Sometimes users flag their own questions to have them migrated to other Stack Exchange sites. Again, there are often "helpful" but don't indicate that the user was doing anything untoward.
But a history of helpful flags indicating to the moderators consistent behaviour which is not tolerated does give the moderators cause to look and see if a suspension is warranted. Let me be clear, even if a suspension is handed out,
the behaviour is the reason for the suspension, not the flags.
If you have reason to believe that a suspension has been unfairly given, you have the option of lodging a complaint with Stack Exchange itself. While a suspension whose time has passed cannot be undone, if the folks at Stack Exchange feel that the moderators have been acting inappropriately, they have all the force to reprimand us (at the extreme end by removing our diamonds and then suspending us). They are also independent from the site-level moderators: their commitment is to Stack Exchange as a whole, and moderators behaving badly can in no way be construed as being in Stack Exchange's short- or long-term interest.