In order to answer this question properly, it is important to know whether you are certain that the bump is new or, perhaps, that it has always been there and you have just not noticed it before.
For example right at the base of the skull where the spine joins in, there is a prominent piece of bone called the external occipital protuberance. This is a normal bone outcropping, and it can be very noticeable if you feel it. However, most of us are not in the habit of closely examining the back of our necks, so when we find this bump it can seem like a new or worrying finding even though it is not. It is especially unlikely that you would have any displaced or broken bone in the next without a history of some accident or trauma and without any pain or discomfort.
There are, of course, other bumps in the next that do need to be checked out. For example, swollen lymph nodes can occur at the base of the skull, although these tend to be soft and rubbery, not hard and bone-like. Of course if you have any fever
or other concerning symptoms following your recent travels, these should also be checked out.
You should show the area to your primary care doctor
in order to ensure peace of mind.