Wrongfully discharged and owe my school $1000 for it, can I do anything?

who ever told you that does not know what they are talking about, first of all you should have gotten the letter BEFORE you took the week off, secondly the only employee a Dr can tell to take time off is his own employees, what a Dr gives is advice no one including you is required by any law to follow his advice, you now have a another condition that can not be proven, I see no hope for you if you can not take responsibility for your actions no one owes you anything and you certainly are in the wrong state to expect anything