I’ve experienced this a few times. Unfortunately, as everyone here has said, these obs tend to be due to serious issues. Grief, heartbreak, panic, depression, that sort of thing.
The longest I’ve cried is about two and a half hours. It wasn’t the same intensity the entire time, but the tears did not stop the entire time. I just couldn’t stop, no matter what I did. Eventually I fell asleep. I also recall two other high-intensity episodes where I sobbed hard for over an hour.
I’ve seen my sister cry during panic attacks and the intensity was scary the first time I saw it. She’s usually a soft, silent tears-down-cheeks kind of crier. One of her recent panicky crying episodes lasted about 15 minutes. Now, 15 minutes is not a particularly long time, but the intensity was unbelievable. Hyperventilating, eyelids twitching, eyes darting all around the room, coughing intermittently, tears flowing at twice or three times the usual volume.
My wife sobs easily, but she has two different sobbing intensities. Her usual sobbing feels intense, but well-controlled and almost “soft”. It’s hard to describe. Like her whole vibe is still soft. She doesn’t seem exhausted afterward. Then she has a more wild, uncontrolled sobbing that feels alarming, and ends up with puffy face, and eyelids and a foul mood. I’ve also seen her sob wildly for over an hour several times. Not fun.