I absolutely agree with you, and normally when we schedule a session that's exactly what I write but this time I didn't want to schedule a session and I don't know why my T understood my email in this way, but if I write just: "No, I don't want a session tomorrow", T will probably think that I am extremely moody and annoying while I didn't just change my mind, it was not my intention from the beginning (i.e. from writing today's e-mail)