I'd guess we might be prone to being either hypo or hyper sensitive to it. I don't find it usually keeps me awake as such. I usually just drink 3 instant coffees a day but I like the occasional latte. I had an incident once though, in a bookshop cafe, where my now-husband, then bf, bought me a latte and got a large not the smallest one which I always go for, which thus had more shots of espresso than I was used to. Not long after drinking it I felt really super excited by all the books in a less calm way than usual, sort of bouncy and fizzy, and chose loads to buy, then in the queue to pay I crashed hard and turned into a virtual zombie barely able to move or speak. Such a weird experience. I hadn't eaten for a while, so it must have hit me harder than normal too. Since then I make sure to only have a one shot latte and try to have food or water along with it!
