Hmm... actually I am not sure what the cancellation policy of my current T is... The previous one had 48h - after this deadline he would charge the full price... I guess that my current T has something similar, here people are really strict and I really do not think that any T would use the sliding scale for any client...
Coming back to the topic - I think I would go to the session with a small cold (if I could hide from my T) as I don't want to miss any session! But if I was pretty ill, I would let know my T about it because I would be too embarrassed that if I came with a flu, she would think that I am so selfish that I don't even think that I could infect her...