[dr_orpheus]

Yeah, I have had this feeling as well. I don't think it is a direct cause of the coffee consumption and is more of an association that the tiredness is still building rapidly at the time you decide you need an afternoon pick-me-up. There is a hysteresis in the caffeine actually kicking in leading to the perception that drinking that cup of coffee in the afternoon is making you more tired.

My understanding (I don't have any experience in any bioscience, just an avid coffee consumer) is caffeine works because it blocks receptors of adenosine which has a depressive effect and is a signaler that makes you tired. While the caffeine is blocking these receptors, the adenosine is still building up. So once the caffeine starts to wear off all of the adenosine comes rushing in to those receptors and you start to crash. Drinking more caffeine after you have started to feel tired now takes longer for the caffeine molecules to start to muscle in and start filling those receptors again. If you can start to clear out the tiredness receptors ahead of the caffeine hitting them it will make the caffeine more effective. This has led some people to start taking a "coffee nap" where you drink you afternoon coffee, immediately take a short nap to help the caffeine be even more effective when you wake up.