Hello So I've Recently Noticed That I Have A Swollen

Hello so I've recently noticed that I have a swollen mastoid process on one side of my neck. The sternocleidomastoid seems a bit swollen as well, but it's mostly the mastoid process. There is no pain or redness or anything like that. I have no fever or anything that would indicate an infection. What could be causing this? Is it something I need to worry about? Thanks.