[Celyn]

Firstly, did you drink much in general the other day? Could it have been that you were perhaps dehydrated?

If not, it may have been caffeine withdrawal symptoms (I was genuinely surprised when I found out this is a real thing). In this case, you could treat it like any other addiction and cut down slowly over a few weeks, rather than stop all of a sudden. Perhaps slowly adding more decaffeinated drinks instead of caffeinated ones. Alternatively, you could stop caffeine all together and deal with the withdrawal symptoms as they shouldn't last more than a few days since caffeine isn't as addictive or dangerous as other substances, so there's no real harm doing that, it's just not particularly pleasant to deal with.