Sometimes laughter is a way of coping with stressful situations. I laughed at my grandpas funeral. I smirked when I had to tell my kids their hamster had died. I also laughed at the event of my own fathers death. It looks bad. But for me it's like the stress of the situation is too much or too uncomfortable that my mind goes the other way so I can cope.

You aren't a terrible person, I am sure there is a valid reason for why you laughed whether it be feeling manic or coping.