The questioning, by itself, is not illegal.  If they are called because of concerns noted by the medical staff, then they have a duty to ask the questions.  The issue with the sedative, however, will determine the credibility of the statements because of the influence of the substances in your system.  I would recommend that you visit with an attorney that routinely handles mental health commitments to make sure that all of the procedures were followed.  From there, you can make a decision on whether or not you want to proceed with a suit for damages.