So I was told today that the Standard Model breaks down at really, really high energies. The lecturer mentioned particles such as electrons hypothetically having energies equivalent to that of entire stars and it got me thinking, surely the maximum theoretical energy any particle can have is limited by the speed of light. I understand I'm talking about only kinetic energy here, but I fail to see how any other form of energy is relevant at those sorts of speeds. I did wonder if massive particles at the speed of light have infinite energy (which satisfies my question if this is the case), but I don't see that sort of behaviour from Einstein's relativistic mass-energy relation.
So my question is- is there a maximum theoretical energy particles can have?