I have a friend who is an adult that takes childrens benadryl (diphenhydramine) if she feels foggy/dizzy, or stressed. how does this help with dizzines and stress?

Sedating medicine: Benadryl (diphenhydramine) is an antihistamine which also has sedation as a side effect. This provides some people a feeling of relaxation. Fogginess & dizziness can sometimes be symptoms of anxiety -- but can caused by other things as well. Getting a full evaluation along with additional suggestions for help would be a good idea. Good psychotherapies (& more effective meds if needed) are available.