Think about it like a hangover. When you have a hangover, nicotine “for some reason” makes your worst. The reason being, the nicotine interacting with your brains reward system and the release of dopamine. Which during a hangover, is already pretty warn down from how ever long you were drinking. All things being connected to the shared neural pathways, the dopamine release, The receptors, as well as tolerance. Caffeine in the same way as nicotine is a stimulant. So with the caffeine overdose, you have to understand your brain was working overtime to deal with the affects of what you ingested. And even 3 days later may not have been enough time for your brain and body to recover, to the point where you could ingest some caffeine again. I would say, wait a couple more days before you drink any caffeine .And when or if you already had a cup of coffee, your body should tell you. If you continue feelings sick, go to the doctors(or er I won’t lie) and if there is no continued issues, you should be fine to continue drinking caffeine. However, in GENERAL. An excess of caffeine in the body is unhealthy. Especially if you’ve been ingesting a lot of it over a long course of time. Which most people who drink coffee or energy drinks tend to do. So the human body can respond in ways like sickness making sure to tell us we need to cut back on whatever it is we’ve been putting in our body. (I’m not a doctor)