A euphoric response of this kind is clearly unstable, and it is apt to collapse and to be replaced by intense grieving. In a small minority of cases, by contrast, the mood may persist, or recur, and hypomanic episodes may ensue.
Bowlby identifies grief-precipitated euphoria as inherently unstable, a precursor either to intensified mourning or to pathological hypomania, not a sign of resilient coping.
, Loss: Sadness and Depression (Attachment and Loss, Volume III), 1980thesis