The good news is that the bump does seem to be getting smaller, which suggests that, what ever it is, it is probably healing up. I don't think that there is likely to be any relationship between the bump and the fact that you get a little light headed from time to time; as you suggest, this is probably more related to your anxiety
about the issue. However, I would definitely recommend that you get the bump checked out. Your primary care doctor
can take a look at it and tell you what is going on, which should help to set your mind at ease about the issue.
By far the most common cause of bumps like this in the mouth are small injuries, like a scratch or nick, to the gums from eating. When this occurs, as part of the body's normal healing process, a small bump may often form, although, as you have noticed, this does tend to get better over time.
A few other common causes of sores or bumps in the mouth include herpes sores and canker sores, which are treated differently. Your doctor can determine whether you have one of these issues and, if so, can prescribe any necessary medication.