Experiments in Espressos (слэш)

2 am - 20 hours without sleep. The experiment may be starting to affect me. Slight heart palpitations earlier -either due to the caffeine or lack of sleep. Maybe lack of food too. Only other possible stimulus could be the barista, but logically speaking, it's impossible for a smile or a brush of fingers as drinks are passed over to have an effect on the circulatory system.
 
 
 
John works the night shift at a 24-hour coffee shop, and meets a mildly sleep-deprived and caffeine-dependent Sherlock Holmes, experimenting on the effects of sleep deprivation on his mind and body.
This is written for the Always1895 September prompt: Coffee Shop.