I recently was hospitalized and missed three weeks of class. I notified my professor while I was in school and when I got out I was told that I needed to supply the university with my complete medical record, sign releases for my providers, meet with the school psychologist and meet with an outside therapist and have them sign a form for the school that included personal information in order to return. I told the school I would send them a letter from my outside doctor stating my dates of admission and that I saw my doctor after I was discharged. The school recieved it and said it wasn't sufficent enough.
I'd go a little farther than my colleagues - ask the university if they have any written policy regarding a student such as you resuming your studies. I wouldn't stand still for someone just telling you what they want. So long as you were a student in good standing when you were hospitalized, they'd have to have a clear-cut reason to deny you re-admittance, and that can't be on an ad hoc basis. The rules may entitle you to a hearing, or otherwise provide for protection of your rights.
I think you should consult with an attorney - preferably one familiar with education law - about this.
I'm only guessing but if you were hospitalized for psychological issues, the university apparently has concerns relating to your safety and/or mental well-being (whether justified or not at this point). I agree with the prior attorney's answer: get a written explanation from the school why it needs your complete medical record and why you need to meet with the school psychologist and an outside therapist.