In my own understanding right now of Nostalgia, it is a happy/good sensation that is felt because of memories remembered from in the past, this is sometimes triggered or randomly occur. For example you could be at any beach, and it could remind you of when you went to the same beach or a better beach in the past with all your friends, and you had a really good time there. Most of the time you remembers these nostalgic memories from a very long time ago, years in fact.

Nostalgia relates to, missing something in the past, which could associate with a person, personalities, things, or even how it used to feel. Nostalgia is closely related to how it used to make you feel, and can be seen through a relation of other people feelings, for example watching your or another kid be exited about something, could cause a nostalgic feeling/memory of when you used to do the same thing. People usually phrase it to be a “good time”, or “the good old days”, and can be experienced through everything like music, games, or even places.

Personally if something is nostalgic it is normally a good feeling due to the processing of stimuli, and something that you do want to remember again. Not something that reminds you of a bad experience.