Described herein are embodiments of systems and a method to identify orthostatic hypotension and postural-orthostatic tachycardia syndrome. One system includes a head-mounted device configured to measure photoplethysmographic signal (PPG signal) at a region on a user's head, and a head-mounted camera configured to capture images indicative of the user's posture. Additionally, the system includes a computer that calculates systolic and diastolic blood pressure values based on the PPG signal, and identifies orthostatic hypotension based on a drop of systolic blood pressure below a first threshold, and/or a drop of diastolic blood pressure below a second threshold, within a predetermined duration from a transition in the posture from supine to sitting posture, or from sitting to standing posture.