Have you ever laughed, only to realise half way through that you're actually sad?

I thought to keep this post short, and simple. Something rarely thought about, but perhaps is more common than first perceived. The trouble is that sometimes we would laugh, only to see that moment will be short lived. Then sometimes we wonder, how can we feel this way all the time? Do others understand this awkward feeling of happiness, and sadness? People laugh all the time at silly things, yet I neither find it funny, nor do I laugh, how can I feel like those people. The greatest worry is that those that accompany you, and share their laughter now will soon leave you, and you will be back to the start. Awkward, worried, confused, and desperate to find purpose in doing even the littlest of things. It's a long drag when you are stuggling to grasp the point of it all, and question whether you even deserve to laugh?