I have treated many terminally ill clients, and ask for a doctors letter, confirming that they are ok to go ahead and have treatments. They are usually coming for something specific, rather than general treatments, so this is what gets okayed. I also use my own judgement as to what is and isn't suitable. I hate the thought of someone who is diabetic for instance feeling like a social outcast because of their condition. I do a wide variety of treatments, so can often find something suitable for them, without the tooing and froing of doctors letters! Obviously, when necessary, it's unavoidable.
But I never give them a form, as that's another trip to take it, leave it, collect it, get it to me! Most clients with conditions that need a letter have a relationship with their doctor that can facilitate this.
Vicki x