Going to the ENT is a good idea. Another consideration is orthostatic hypotension, when someone gets lightheaded feeling when the body position changes. My brother-in-law has it, similar symptoms that you mentioned.
I looked it up on the web to make sure I got the name right, and found there a way to check for it:
Orthostatic BP Measurement:
Measure BP and heart rate while lying down (after 5 minutes of rest), then immediately upon standing, and again after 3 minutes of standing. A drop of ≥20 mmHg systolic or ≥10 mmHg diastolic confirms orthostatic hypotension. Although of course you’d want to see a doctor.
Who knew there was a test for it!? I always learn something new when people pose a question on the forum.