I have worked for the same company for 22 years. Up until 3 years ago, I was a respected, valued, and sought-after employee. Then, on top of my chronic back pain due to a failed surgery, I fell (not at work), hit my head and suffered neurologic consequences including narcolepsy, other sleep disorders and short-term memory-loss. After transferring to a new job, I was disciplined several times for attendance and once for missing an appointment. In March my car broke down, whilecalling my first appointment for the day to let them know I couldn't make it the tow driver arrived and I said I would call them back to reschedule. I forgot. Several weeks later they contacted my manager. Last week a customer called to complain that he left a message 3 weeks ago and I never returned the call. I never got the message. We did have problems with our phone system during this time... I am now being removed from my current position and put on PIP for 3 months. Who hasn't fogotten to call someonen or missed an appointment? I have proof that my MANAGER missed an appointment once as I had to make up for it and the customer actually told me he called to say he couldn't make it and then never called back! I feel that they are tyring to get rid of me because of my medical conditions. I don't know what to do.

No, you are being given warnings and actions against you because of continued behavior issues and lack of ability to do the job. One missing a call is one thing but that added to the other issues, all make a history, Your boss, did not miss all the other things. Yes everyone misses a call but failure to call back is not acceptable in business, but then someone covered the boss, no one covered your lack to call back.

The company does not have to allow poor work performance, they can, if possible make accomidations to help you do your job, but most of this deals with physical issues.

You can ask for a job without as many memory requirements but it appears they have been working with you

You need to work on a system, where you stop missing things, and understand importance, such as appointments and less on tow truck driver, who could have waited on you