SunshineCleaning
I'm 37 and I'm in exactly the same boat as you - got a heart problem and I'm on Beta Blockers for it but this makes my already low blood pressure even lower. Doctor told me to stay off of ladders.
All my customers know I've been unwell with my ticker so I've just turned up with my pole and carried on as usual - if they've been home, they've come out and said that they're glad that I don't have to go up a ladder now and I've briefly explained how the system works, and if they've not been home, I've just done them with the pole and made no mention of it on my 'Windows Cleaned' slip and (I'm not exaggerating) I've had so many letters with the cheques saying how they've never looked cleaner (obviously because the frames are now clean).
I've faffed around thinking about changing over for two years now worrying what my customers would think but I've got to a stage where I either do it or find another job - so I've just gone for it.
The only things I've said to my customers are that everyone has been happy with the new system and really supportive (and they have), it may take a couple of cleans to come up perfect as I've got years of detergent to get out of the frames and the only difference they will see is that I leave them wet, but they dry clean.
Everyone has been so supportive. I think there is a case for giving letters of explanation, but I think you can over complicate it for customers. If you've got a good set of customers, they'll be fine.
Hope this helps.
Matt.