All dreams come from the subconscious mind, but what that means is that they can represent anything from a deep-rooted fear or anxiety to something as simple as dreaming of your favourite band, or something you ate for lunch.
There are times where a one-off dream can hold a lot of meaning and can revolve around a certain issue that's been haunting you. It won't be re-occurring because whatever it was has been resolved by that one dream, or the issue was resolved in your day to day life soon after. In the same way a lot of one-off dreams are really nothing to worry about, because they tend to represent problems or issues that aren't really big and you quickly forget (like an argument with a friend or an test you just did). And some dreams don't really mean anything and just revolve around whatever is lingering in the back of your mind.
The only dreams worth analysing are re-occurring ones, because they represent an issue that hasn't been faced or resolved yet, and is big enough that you don't forget it quickly.