From the point of view of pathological and normal physiology, positive and negative emotions cause exactly the same processes in the body. The most obvious change is nervous excitement, i.e. accumulation of nerve impulses (from the point of view of physical chemistry - electrical charges). Excessive arousal is what causes stress, the pathophysiology of which has been described in detail in many works, starting with Hans Selye, who introduced this concept.
Yes, if by stress we mean the totality of non-specific adaptive normal reactions of the body to abrupt changes in the homeostasis of the body, as well as the corresponding state of the nervous system of the body or the body as a whole. Strong emotions arise in response to changes in the organism-environment ratio and are manifested in biochemical changes, therefore, they are both a deviation from homeostasis and its consequence. Regardless of the sign.
Psychologists distinguish the concept of positive stress - eustress, and negative stress - distress leading to various diseases if it lasts too long. So, whether a positive emotion, or whatever, will be a source of distress depends on many factors, including the person's attitude to their own emotions and stress.
There is an interesting video on TED.com - "How to make friends with stress" ted.com