I definitely don't think this is legal (disclaimer though: I am not a lawyer), unless your manager is also a MD, but even then, I don't think it's legal unless he's acting in that capacity.

If, as you note, you are no longer working there, I wouldn't worry yourself too much about it unless you think that you do have focus issues. If that's the case, I would try correcting the problem in non-medical ways first. There's a number of things you can try - keep a tidy workspace, listen to soothing music if possible, try meditation, keep a low sugar diet, etc. If you feel that you've expended your options, consult your doctor.