Why can you laugh to tears?

In life, if a person meets something that makes you very happy and excited, he will definitely laugh, and if you meet something funny, you will also laugh and cry. In my impression, tears only come out when I cry, so why do I cry when I laugh? Tears are often secreted and always flow on the surface of the eyeball. We usually secrete less tears, which flow regularly along the small gap between the surface of the eyeball and the inner surface of the eyelid, so you won't feel the tears flowing. However, when you open your eyes and close your eyes, the tears on the surface of these eyeballs are sucked into the sewer of tears-nasolacrimal duct. When people laugh loudly, the pressure in the nasal cavity will increase and the flow of tears to the nasal cavity will be hindered. On the one hand, when people laugh, they will close their eyelids tightly and squeeze tears into their noses. On the other hand, the nasolacrimal duct will not flow downwards, and the tears accumulated in the eyes will be full, so you will cry when you laugh.