Remember not to leave a sheet mask on the skin for too long. 10-15 minutes is sufficient for the skin to absorb all the essence essential for the skin.
Leaving a mask on for too long can have reverse effects as it soaks up moisture from the skin back to the mask - think diffusion principle: moisture moves from high to low concentration. If your skin is soaked up with moisture, and the mask is dry, the essence will move backwards.
So next time, remember to look at the time when you put on your mask. If the mask sheet feels dry because of your dehydrated skin, remove it earlier than the stipulated time.