Bah!
So I didn't get to sleep when I wanted, but I did do some useful thinking. Yoon's comments have set me to thinking that it's difficult to get a mystery to work in 6,000 words, particularly one that needs a significant amount of character background, and that really needs additional suspects (the mystery as it stands is "why did my ventilator fail", with the denoument as "Oh, actually that was an attempt to kill me, whoa!", whodunnit is obvious from that point). So the answer is probably to set it on the back burner, and let some additional sub-plots and characters ferment, then address it at longer length. One option is to pull it back to being near contemporary, rather than an undefined amount of time in the future, effectively shifting it into detective/technothriller rather than SF.
In other news, with the snow gone I managed to get out for the first time in a week and get some shopping done. Asda's sliced bread aisle appeared to have been stripped by locusts, though their in-house bakery was fully stocked. It looks like deliveries hadn't been getting through, which is a bit surprising when it's 2 minutes off the M2 and on a main road.
( Cut for (Virtual) Nature, Red in Tooth and Claw )