I sleep 10 hours a night but still need to nap constantly during the day. Even 400 mg of caffeine doesn't buzz me, it just makes me feel 70% close to my normal, high energy 20s self. My daytime fatigue is so severe I've been mistaken for being drunk (even though I don't drink), and I experience a dream like brain fog around friends unless I use caffeine pills to seem present.
I know this is part of normal aging for a woman in her 30s, but it's frustrating to constantly need naps when I haven't even done anything. Sometimes you just have to biohack. Still, I feel a bit jealous of how men age differently and seem to keep loads of energy.
It sounds like you built up a tolerance and would benefit from quitting caffeine altogether. The first week or so will be a groggy hell, but once you adjust, your baseline will be much more alert.
I don't have caffeine often, it's only when I'm on outings.
How often do you go on outings? When did the symptoms generally start? Was it around a time you started taking caffeine or taking more of it than before? Are you on other psychoactive medications that could affect your brain?
Regardless, if you're taking such a large dose of caffeine even occasionally, it could drastically affect your adenosine receptors, and that's only going to cause tiredness, speech slurring, brain fog, etc to continue EVERY day until you've been without caffeine long enough for them to return to a baseline.
Personally, I'd suggest slowly decreasing your caffeine intake. Most people say "just quit taking it" but that can lead to some really annoying crash and withdrawal symptoms, so I'd say slowly reduce by maybe ~50mg per dose, each week or so, until you're around 100-200mg max on any given day. If it doesn't work out, you can always go back to your current caffeine intake, but if it does work out, you've just saved yourself a big headache and potential medical problems.
I can promise you, this is not a normal bodily reaction to have at your age, and you're already hitting the recommended safe human limit if you ever take 400mg. To be clear, I'm not here to judge you. Just like most other people here, I think we're all just quite concerned for your health and safety.