This hair evacuation-thing qualifies as one of those pregnancy/postpartum things they don’t tell you. So, well, now you’ve been told.
As you can see, in the grand scheme of things, a little hair loss is really not that a big deal.
Update: 2 weeks later and I'm down to only one hand-full of hair collected post-shower. I'm not sure how much longer I can sustain the 'great hair evacuation' without going bald! Does this photo gross you out? Sorry about that. I had to document it because it just baffles me every time.