The first time I received a shiatsu session, I felt an overwhelming rush of emotion! I've never felt anything quite like it. My head and body felt light, and I wanted to burst into tears (as I tend to do quite easily).

I think it's important to feel as ease during each session, and to trust your therapist. Shiatsu is a practice used to release tension and anxiety, so if you are feeling anxious about it and unable to release your emotions, perhaps that is something you could work on.
And if you continue to struggle, perhaps shiatsu just isn't for you.

Do not feel as though you have to force or hold in any emotion; just be natural and enjoy yourself!