At a very basic level I know that gravity isn't generated by mass but rather the stress-energy tensor and when I wave my hands a lot it seems like that implies that energy in $E^2 = (pc)^2 + (mc^2)^2$ is the source of gravity.
If the total energy of a particle contributes to the generation of a gravitational field, that seems to imply some strange things. For example, you could accelerate a particle like an electron to such a high velocity that it has enough momentum / kinetic energy to collapse into a black hole. An observer traveling with the electron would see an electron and stationary observers would see an arbitrarily massive black hole flying by. These observations seem to be contradictory. The same would be true of an extremely high energy photon.
Another consequence is that a stationary particle could appear to have so much mass that it could attract / deflect the trajectory of a rapidly moving observer. It seems odd that at low velocities you wouldn't even notice a stationary electron as you pass it by but at high velocities the gravitational field you observe could be significant enough to alter your path.
Am I correct that non-mass-energy generates a gravitational field? If it does, how are these strange observations like a particle looking like a black hole in one reference frame but not another reconciled?