It happens. I fell from 2300-1800. Worst losing streak I've ever had. Luckily, been holding between 2400-2500 lately, but as soon as I hit 2500 I seem to get people that pick characters they have almost no time on or just aren't that good with them.
Hell, just played one of my best games ever as 76, leading in elims and damage by a decent margin, team complains we have no 2nd healer. I end up swapping, we get 2 ticks, and the round ends. Next round, I'm suddenly solo healing, asking my team to help me out because I'm running/flying everywhere as Mercy trying to avoid the monkey and flying squirrel that's chasing my ass.