Chairs are sneaky little things. You get yourself perfectly positioned, feel like royalty at the exact right height, and then somewhere between your second paragraph and third tab open, gravity starts winning. Slowly. Quietly. Without a single apology.
Scientists will throw around phrases like "hydraulic cylinder wear" and "nitrogen gas pressure loss" but that all sounds like a lot of effort to explain something way more obvious. Your chair is reading the room. It detects the drop in caffeine circulating through your system and responds accordingly. No coffee, no structural support. Simple cause and effect.