Have . Have you been staying on your feet a lot lately? It could be that it's from standing on them too long which causes the blood to stay there more and not be able to circulate back to your body more efficiently. If it is only one-time occurence, you should try to just soak your feet in lukewarm epsom salt water and the swelling will go down. If the swelling has occured more than one time, then it's better to discuss this with your physician. It could be coming from hypertension or venous insufficiency.
Foot . Foot swelling without trauma can be due to a variety of issues. First of all, is the swelling the same on both feet? If so, this points to a more systemic cause, like cardiac disease, vein disease, or lymphedema. If it is unilateral, or one sided, the cause is usually more localized, and things such as gout, deep vein thrombosis, or other local process should be considered. Your pcp would need to be seen to make a more informed decision.