4 year old is wetting bed again?

Again? If you child was dry at night and now is wetting, something is wrong. Although it could be anxiety, there may be physical issues such as a urinary tract infection. Best to call your pediatrician.
Not unusual. Many young children start wetting the bed after being dry for a period of time, so there is usually no "medical" problem. However it is worth having the urine checked to rule out an infection, diabetes or kidney problem. Cause could be an upset, such as pet dying etc. Suggest stop fluids after supper, could try waking to use br when you go to bed. Good luck!