Losing a little bit of hair in the shower is normal and nothing to worry about but you shouldn't be losing a lot of hair when showering.
If you start losing too much hair when showering then it's not normal and the hair loss could be caused by stress, anxiety, hormone imbalances, Thyroid Problems and even a change in a persons diet.
If you're losing more than just a little bit of hair when showering then it would be a good idea to consult your doctor so they can see if something could be wrong that could be fixed.
Losing some hair in the shower that makes clumps is normal but a lot of hair falling out in the shower is not normal.