  Extended quantum mechanics using non-Hermitian, pseudo-Hermitian Hamiltonians
is briefly reviewed. Supersymmetric regularizations, solvable simulations and
large-N expansion techniques are recollected as suitable means for the study of
non-local quasi-particles. Their many-particle or even, perhaps, unstable and
decaying generalizations are also considered. Picking up the Klein-Gordon
equation and its Feshbach-Villars' Hamiltonian for definiteness, we argue that
the PT symmetry might help to clarify experimental aspects of relativistic
quantum mechanics.
