  We discuss how introducing an equilibrium frame, in which a given Hamiltonian
has balanced loss and gain terms, can reveal PT symmetry hidden in
non-Hermitian Hamiltonians of dissipative systems. Passive PT-symmetric
Hamiltonians, in which only loss is present and gain is absent, can also
display exceptional points, just like PT-symmetric systems, and therefore are
extensively investigated. We demonstrate that non-Hermitian Hamiltonians, which
can be divided into a PT-symmetric term and a term commuting with the
Hamiltonian, possess hidden PT symmetries. These symmetries become apparent in
the equilibrium frame. We also show that the number of eigenstates having the
same value in an exceptional point is usually smaller in the initial frame than
in the equilibrium frame. This property is associated with the second part of
the Hamiltonian.
