To provide a scientific reason for this is that zopiclone is pure alpha BZD containina alpha 1 subunit agonist, which whould enhance synaptic dopamine levels. All the other benzodiazepines are just relatively nonselective in their agonism of the receptors so they can sometime elicit this effect, the z - drugs and alcohol and barbiturates have a much higher incidence of these types of side effects.
To estimate to the risk, you really can't, as it extremely high in individuals very prone to those behvaiors anyway (which isn't really common is it?) on high dosages of amnestics - anticholinergics, benzodiazepines, barbiturates, ethanol, etc., to low to non-existent in others.
It runs the gamut. It's just variable.