HRT patches... has anyone had breakthrough hot flushes while using patches?

I have been very successfully controlling hot flushes using HRT patches for almost 18 months. During the last month I have experienced breakthrough hot flushes a day or two before the patch is due to be changed. Has anyone experienced a similar thing, what causes it, does it improve, why me? Because I am only able to move my head I have no way of adjusting bedding at night, I have assistance for several hours during the day and early evening but spend the nights here alone and value that measure of independence immeasurably. Using HRT has worked wonderfully up until now. If anyone with a similar experience has a suggestion to make I would welcome the input.