What Causes Brief Episodes Of Blocked Nasal Breathing, Dizziness, Head Tightness, And Darkened Vision That Resolve In Seconds?

Hello, good afternoon, so ever since the beginning of this month I’ve been experiencing dizziness, first I can’t seem to inhale air and when I try i can’t inhale through my nose like if something was blocking or preventing me from inhaling, but after that goes away after a few seconds I can inhale fine. After I can’t inhale for a few seconds, about 5 seconds later my head starts feeling tight and my vision sort of goes away like blackness is taking over my vision. It only lasts for a couple of seconds and then I go back to breathing in and seeing normally. It’s happened twice this month and whenever my vision starts to darken I fear that I might be dying, what might be the cause? Please help