I bought a battery-powered BP and pulse measuring thingy last year when I started getting dizzy while exercising (doh!) I usually get pretty normal readings when sitting and right after standing, but after 5 minutes of standing I always get an "ERROR" reading, and it looks like it's picking up my pulse very irregularly while it's inflating (it flashes each time it gets my pulse). But if I try it a 2nd or 3rd time in a row, it gives a pretty normal value. And if I wait a few minutes, it's always "ERROR" again. It sounds like the typical CFS circulation problems can make the pulse difficult to detect (especially when standing a bit?), but why would it get normal readings after failing a time or two with no break in between?