Can my medical records be disclosed without my informed consent at the time of treatment?

Yes.

The Amended HIPAA Privacy Rule states only that you must receive a Privacy Notice telling you how your personal health information will be used and disclosed. Section 164.520(c) (2) (i) (A).
Privacy Notices are often mistaken for consent forms, but they are simply notices telling you what will happen to your medical records.

Example: information about a depressed person’s attempted suicide and hospitalization can be used and disclosed without any notice to him/her without his/her consent and even if he/she objects.