Thanks for using health health acre magic for posting your query.
From the kind of description you have given it appears that the lump was actually a hemoatoma, a collection of blood. It generally doesn't cause any problem and resolve on its own. The indentation may be cause of the surrounding oedema.
You should be concerned about it if it becomes unusually painful or you develop fever
which in case will happen if it becomes infected.
Otherwise, there is no reason to worry!
Hope I am able to solve your concerns.