question: im 15 years old. ive had mono about three years ago and sometimes i feel like the symptoms come back. i feel tierd but idk if its just because its summer but persistant symptoms are when i stand up to quick or after siting or a long time i start to blackout, feel my chest tightening and feel like i cannot breathe for 2-5 seconds depending how bad the tightening feeling gets. sometimes i also feel a little dizzy but that comes and go with my tiredness. any ideas?