Sounds like very strong coffee …… ! , I always try to drink lotsa water after coffee, even if I need to stay. Near the W/C for hour afterwards , or dilute it with food . It does seem to act like a upper to the nervous system.
Am not sure am qualified to answer that ,about instant coffee . I went over to decaf coffee beans that were of a strong dark roast, so I did not lose the flavour of coffee.