Diphenhydramine (Benadryl) is an H1-antagonist, with unfortunate anti-cholinergic side effects: dry mouth (xerostomia), dry eyes (xerophthalmia), and also including urinary hesitancy and inability to void.
I would presume to think that the next best action would be to evaluate the bladder for bladder distension.
If overly distended, then a urinary (foley) catheterization may be warranted to void the patient. However, ordering a Foley first may be an unnecessary, uncomfortable, and likely painful procedure.
After examining the bladder externally (suprapubically), then fluids may be warranted.
The answer is : the primary laws of reflexes
The fact that each plant gets only one allele
from each parent plant is detailed in the law of segregation
The normal force is greater than the force of gravity