One of the most common symptomatic complaints after COVID-19, vaccination, and now in most persons who have both exposures is POTS (postural orthostatic tachycardia syndrome).
This is a disorder where there is a lack of synchronization between the heart, brain, spinal cord sympathetic chain of ganglia, adrenal gland, and the blood vessels both arterial and venous. The Spike protein on SARS-CoV-2 and flooding the system after vaccination damages neurological tissue, the adrenal glands, and the heart.