Am I obligated to fast two consecutive months as expiation for abandoning prayer, knowing that I suffered from obsessive-compulsive disorder and do not remember how many times I swore and vowed to abandon prayer?

An expiation for breaking an oath is incumbent upon you due to your breaking the oath, and also for not fulfilling the vow, which is a vow of obstinacy. A single expiation is incumbent upon you for repeating the oath concerning one thing, unless you broke the oath, then swore again, then broke it again; in which case, an expiation is incumbent upon you for each time you broke it. If you do not know the number of oaths, then investigate and act upon your best judgment. If the oath, the vow, and the breaking of the oath occurred under the influence of overwhelming obsessive thoughts, then nothing is incumbent upon you, because the person afflicted by obsessive thoughts is considered as if compelled, and the divorce of a person afflicted by obsessive thoughts does not take place if it was not intentional.