I would suggest that if your therapist doesn't offer you a blanket or a comforter during your sessions, that you bring your own. Everyone has their own internal thermostat, and it differs among us.

The water temperature during inflow should be just about 100-101 degrees F. Most people can detect a temperature drop of even one degree below normal body temperature, and many consider it to be uncomfortable if continued for more than a few minutes. Lowered inflow temperature is often used to help stimulate release and cause the muscles of the colon to contract to assist in tonifying the colon.

But your therapist should be willing to go out of her way to make you comfortable during your treatments. If not, perhaps it's time to seek out another therapist.