Just opened a 20+ odd grams of the Nescafe black coffee yesterday and attempted to drink it finish in 1 cup. Bad idea. Ended up having a caffeine overdose. Which lead to one whole day of no sleep, heart beating much faster and indigestion. Heart burn? Running toilets. And feeling cranky because of all the symptoms above. Took me to almost 24 hours before I could get some sleep.

Another link to look at?

https://www.healthline.com/nutrition/caffeine-side-effects#section3