This can mean that you find your own jokes funny, and laugh at them, regardless of those around you not being affected. It could be due to your sociopathology. You might be downright uncouth and undeserved of any positive reactions. Whereas group laughter is a form of cultural agreement, and of similar bonding strength as supporting equal sports teams, or liking equal music.
Sometimes, spontaneously laughing can diffusion a situation which might have been embarrassing. It does so by acknowledging the embarrassment and removing the sympathetic discomfort of those around. It’s a display of humility, turning a possible minus into a plus.
Then there’s laughing whilst physically alone. I think this is a sign that you’ve reached a “living in the now”, where you’re not brooding very much about the past you can’t change, and the future that hasn’t even happened. Pointless and unhelpful thought patterns are common in developed countries. However, if you’re an Amazonian hunter, poison darting your food from the canopy of leaves and branches above you, you don’t worry about the past, or whether the monkeys will get wise to your blowpipe and move out. This life is much more straightforward.
The end of my “I am” book strongly criticises us having excessive numbers of choices. It cites them as a great problem in developed countries. We’re complicating gender for example, and it has become a very contentious political issue now. Amazonians have very few options, and certainly not ever, ones like gender. When our minds are not continuously bombarded with choices, they can settle into a mode that works. Mother nature will make many of the jungle dwellers decisions for them, and by trotting them out over the course of the seasons and annual cycles, their reactions and behaviours will reach a natural and reliable states, as if by gravity. The existence of their basic human needs, à la Maslow’s pyramid, are the simple proof of it, and are mostly bottom tier features. The higher tier western things around technology and politics, etc., don’t feature in the jungle.
So, what has this got to do with laughing alone? Well, laughing alone is about emptying our heads, not of memories, but of endless considerations. Some people meditate. I’ve played classical piano for 34 years up to now. I think we can help our minds become more nebulous, and/or subjective, or less analytical, and with any advanced skill at a reasonable level of mastery. As it happens, I’ve noticed I now struggle with mental arithmetic. I’m 55, but in my twenties, whilst I was working as a C programmer, without writing notes down, I could juggle half a dozen algorithmic thoughts in my head at once. Imagine me unleashing that mental power on my life problems that I couldn’t actually solve !
Software needs to be bug-free, unlike life, which probably should never be perfect, as that might cause stagnation. However, my older brother’s continued coding, ultimately in Cambridge, the “Silicon Valley” of the UK, has led to him, and many other professionals in the city, to suffer from obsessive-compulsive disorder, and it should be no surprise that some leading OCD specialists, have made the area their base.
Here's the thing: humour enters us, and we can laugh alone to ourselves, after troubles exit our mind: the pointless ones. There will always be trouble, but worries about the past that has passed, and the future that might not even happen, make the most fun people seem dull !