  Unconventional nonequilibrium phases with restricted correlation spreading
and slow entanglement growth have been proposed to emerge in systems with
confined excitations, calling their thermalization dynamics into question.
Here, we show that in confined systems the thermalization dynamics after a
quantum quench instead exhibits multiple stages with well separated time
scales. As an example, we consider the confined Ising spin chain, in which
domain walls in the ordered phase form bound states reminiscent of mesons. The
system first relaxes towards a prethermal state, described by a Gibbs ensemble
with conserved meson number. The prethermal state arises from rare events in
which mesons are created in close vicinity, leading to an avalanche of
scattering events. Only at much later times a true thermal equilibrium is
achieved in which the meson number conservation is violated by a mechanism akin
to the Schwinger effect. The discussed prethermalization dynamics is directly
relevant to generic one-dimensional, many-body systems with confined
excitations
