Is a fire alarm bad? Not if there is a fire. That is what it is there for. You call the fire department, they check it out and either put out the fire or tell you it was a false alarm. Then they reset it. This is how it is supposed to work.
Nervous systems of course are much more complex, but the principle is the same. An emergency–or what feels like an emergency–emerges, and in a healthy system awareness is maintained, resources, particularly calming resources–are deployed, and a healthy status quo que ante is reinstated.
PTSD is not a fire, but rather a fire alarm that cannot be turned off. The fire was long ago.
And on a slightly different note, could one not argue that sadness can be an EXPANSIVE emotion? In feeling your own pain can you not feel that of the world? Where could compassion arise except with an honest feeling of, and processing of, through kindness and gentleness, ones own loneliness, brokenness, and silent fears?