Even if you are disguising for a good reason and even if you are doing it only momentarily to serve some other purpose, the bottom line of it is, you are using it to hide who you are. Now that this is understood, it will make interpretation of that dream a bit easier.
If you have a dream about a disguise then you need to know who was wearing the disguise in the dream. If your dream involves a world where everyone is in a disguise then this means you feel like people around you are not being honest with you, that they are putting up a front when you are near for some reason. It could very well be that you have surrounded yourself with the company of dishonest people and you are now wishing you hadn’t but on the other hand it could just as easily be that you have trust issues and you need to be as objective with that possibility as you can or else you run the risk of becoming even more narcissistic and untrusting.
If you have a dream in which you see that you are wearing a disguise then it means that you do not trust yourself nor do you trust those around you. You are trying to hide your identity and your inner thoughts from other people because you don’t want them to know who you are. Try opening up and sharing more, the life you lead will be much less guarded and much more fruitful because of this later on.