There are many results on the Wild Magic sorcerer's Wild Magic Surge table (PHB, p. 103) that says "centered on yourself". For instance:
07–08: You cast fireball as a 3rd-level spell centered on yourself.
[…]
13–14: You cast confusion centered on yourself.
I'm not sure if that means that the spell originates from you as normal, or if the spell affects only yourself (that doesn't make much sense), if its cast as an area spell, or what exactly it means.
Best Answer
The spell's area of effect is centered on your location
Both of the mentioned spells have a spherical area of effect, centered on a specific point. For example, fireball says (emphasis mine):
When the table says "centered on yourself", it means that instead of "a point you choose", the spherical area of effect is centered on you. In all other respects, the spell functions as it normally would. For a fireball, this means that you are hit by the spell, as is anyone within 20 feet of you.