The influence of highly energetic electrons and nonstationarity on the H‐like resonance line and its adjacent He‐like satellites 1s21‐2121′ are investigated. Both of this effects result in an additional population (besides the dielectronic capture channel) of the autoionising 2121′‐levels through the excitation from the metastable levels of single excited He‐like ions. This channel can be rather strong especially for double excited levels with low rates of dielectronic capture, which are widely used for density diagnostics. It is shown, that the neglection of the non‐equilibrium plasma state and the excitation by highly energetic electrons can result in serious overestimations of the electron density and temperature. Fully time dependent simulations are carried out for an experimental aluminium spectrum from a low inductance vacuum spark. We show that effects of highly energetic electrons and nonstationarity provide electron temperatures two times lower and electron densities an order of magnitude lower than simulations based upon thermal‐equilibrium interpretations.