Firstly, you dont have to be scared. It does not seem to be a serious condition. From your description the possible reasons could be as below;
As you say it disappears when you yawn and close the nostrils it could be related to a condition called eustachian tube dysfunction
. This is a tube which connects ear to the back of the nose and helps in normalising the pressure in the middle ear cavity. If the tube is not opening properly or lax, it could lead to pressure changes which gets relieved when you yawn etc as the tube opens up by doing these actions.
Whenever the ears get exposed to loud music there could be temporary hearing loss
which gets back to normal in hours. So avoid exposure to loud sounds.
If the symptoms persist and you have a decrease hearing along with ringing in your ears, please visit an ENT specialist