Thank you so much for the lengthy reply. Despite what I typed, I think I've been maybe a "typcial runner" and ignored all sensible advice (which is v bad) and still try and run. Since I last posted I've managed a 6 and a 4 mile run and kept them v slow and v flat & walked up any hills. I have then pretty much rested the rest of the day and made sure I've had an early night. So far, all is okay...I've finished my antibiotics now and am taking lots of stuff to boost my immunity - stuff from the homeopathic and elderberry tablets.
I think your advice about maybe only doing one 20m run is sensible....my aim is really to get round and say that I've done one. But I need to continue to listen to my body and if I need to defer, I should do that. I certainly don't want to end up like your friend with a year of feeling unwell. Last time I had pleurisy, I certainly felt much iller and still ended up taking 4 mths off.