Presyncope describes a feeling of lightheadedness as though one might blackout, but consciousness is preserved. The most common cause of presyncope is a sudden fall in blood pressure. Less commonly, presyncope may be caused by heart rhythm abnormalities, such as a pause in the heart beat or racing of the heart. These problems may be solely due to problems with the heart’s electrical system or associated with disease of the heart muscle or valves.
Presyncope/Syncope, Auckland Heart Group, https://www.heartgroup.co.nz/Patient+Information/Cardiac+Conditions/Adult/Adults+-+PresyncopeSyncope.html