a question about downswings

[Adam22]

i recently started playing 10/20 with my appropriate 6000 dollar bankroll. i did well for my first 25,000 or so hands and was maintaining about 2bb/100. then this week i hit a massive downswing and lost all of my profit as well as another 50bb... my question is how unusual is that? i know 300bb is supposed to be sufficient... however within this downswing i've seemingly went from 600bb to less than 300bb which seems really unlikely. this whole thing has me kinda spooked in the head even though i'm essentially 100% confident in my play throughout it.