That could not be frictional forces, but Kinetic Energy would convert to classical Potential Energy or Mass Energy instantaneous.

The real problem is whether:

KE + PE = 0

as assumed by Einstein in his GR Lagrangian and led Hawking to conclude that every came from nothing, or

KE + PE = mc^2

where KE has to equal the sum of which in my view would make a lot more sense.

If you consider total kinetic energy as mv^2, then PE = m(c^2 -v^2)

If you then divide through to get natural units then you get (1-v^2/c^2), and I cannot help but think that I have seen that somewhere before.