You all keep mentioning hangovers from this stuff. . . Most people here seem unaware that Apfelwien is typically mixed with sparkling water when it is served. Particularly in Frankfurt - any classic apfelwein place (like Wagner's) brings you a bembel (like a pitcher) full of apfelwein, and a bottle of sparkling water.
You generally start with about a 50/50 mix, and will likely use less water after you drink a few glasses. The mix is partly why I never get a hangover from apfelwein. . . Though on a hot sumemr day I prefer to just fill a pint glass with ice and then top it up with straight apfelwein (still achieving a mix).