That feeling of "running out of fuel"

That feeling of "running out of fuel" Hi! ​ To give a bit of background on myself, I began stuttering as a teenager. It also peaked in those years; gone is the anxiety, the repetition of syllables, etc. Now I have a subtly different problem. ​ Say I'm with a good trusted friend. I can have fluent talk and banter with him for about 2 hours. After that, fluency starts to decline steadily. But it's never caused by some kind of anxiety; instead I can directly feel that I'm "running out of fuel" in my brain. ​ It's the same feeling I'd get when I'm underslept, overworked, or I haven't eaten or hydrated properly. ​ So, when this feeling starts, I cannot start phrases as effortlessly even though I'll be barely anxious. Generally I'm even open about the fact that I'm tired and beginning to stutter. ​ I wonder if this is a somewhat common dynamic. I try to avoid it by living a healthy lifestyle (addressing the mentioned sources of 'tiredness'). But it's not being enough. ​ In prior years I didn't have only two hours of "fuel" per day. Do you think there are measures I can take *during social interaction* to avoid ending up emptied? ​ I've tried caffeine in the past to no avail; lately I'm trying snacking and casual water drinking. Still unconclusive.