Right before breathlessness. When I'm laughing so hard my muscles ache, and no more sound of laughter comes out, the tears start to flow. My nose starts to run. I assume my face turns red. I can feel blood pooling in my forehead and cheeks. There is no sobbing or anything. My face is just scrunched up and leaky. Soon after this stage, it becomes difficult to stop laughing and shaking long enough to inhale. Literal hysteria at this point. If it goes on long enough, I may panic. Panic will halt the giggles so I can breathe. But I usually don't stop laughing for long. I get a few breaths and the laughter starts over. It feels good, overall, to laugh that hard. Has to be pretty fucking funny though.