Glad to hear you are feeling a little better. Unfortunately from what Ive found, ME changes over time.. you could of just entered like a new phase in the illness. I can rarely get PEM nowdays as the OI triggers off things bad before I can even over do it with activity. As far orthostatic narrowing of the pulse pressure goes.. Dr David Bell defines it as an issue (unless he's changed his views) as when the narrowing pulse pressure gets down to 18mm Hg or lower. My BP monitor must be a bit better then yours as mine dont error out with the narrowing of pulse pressure till theres under 7mm Hg difference with the two. (its shows up my pulse pressure narrowing well till then) What Ive found my BP monitor really hates (and all the other monitors Ive used seem to really dislike this too) and will easily error it out, is if I start getting arrthymia beats (dysregulated beating). The monitor then is trying to come up with heart rate for a one minute period.. dysregulated beats completely screw the monitors up and one keeps getting Error results. Many monitors actually say in their manuals that they arent suitable for those with arrthymia. Consider it may be arrthymia rather then narrowing of pulse pressure screwing your monitor up. Arrthymia isnt all that uncommon with OI.