I went to fetch a bottle cage from the bike parts shed.
Pulling it out I snagged a tyre which was on a hook.
That caught one of the shelving units, which fell on me.
As it fell that caught a second shelving unit, which landed on the first.
SWMBO eventually wandered outside to ask if I was OK having heard me shouting.
I'm now dis-entangled but dazed as that first parts shelf landed on the back of my head/neck, compounded by the second unit.
All because son no. 2 lost his bike's (new) bottle cage on the retro ride we did this morning, saying "it fell off somewhere back there"