How old are you? I’ll assume from a quick profile check that you are trying to drop fat, are you doing a lot of cardio? Maybe that’s running you down.
If you have a mid-day slump it is either:
chronic under sleeping (or not enough quality sleep) issues…usually caused from chaotic under then oversleeping. In which case no caffeine and try to get some semblance of structure.
diet related- from sugar dipping post workout or caloric restrictions overall…or maybe eating a ton of simple carbs at once
hormone changes- not sure your age but teens are all over the map with energy and growing…totally up one minute and napping the next, it may pass.
So what do you think it is?