My therapist doesn't charge if I'm ill or if I give 48 hours notice. Usually we'll reschedule if possible (sometimes she would squeeze me in by shifting her paperwork time around). This happened a lot when I was having last-minute schedule changes because of the timing of fertility appointments. I have only canceled once because I was angry and didn't feel like I could engage with her while also hanging onto my mental stability. I gave enough notice so she didn't charge then anyway.