Where would you prefer to collapse, your room or the road? For a stairway is really a road, and this one has heavy traffic, but...
But you do not choose when, you do not choose where, you do not choose who triggers it.
This is why Marlowe is sitting at on the landing of one of the stairs on one of the floors, head against the wall and eye closed. One leg drawn up, the other foot resting on the second stair down; he could just be thinking.
People's knuckles aren't normally so white when they do that, though.