I'm sorry. "Nor" is wrong. The sentence as you've written it means
"Stress is normal unless it is excessive, and [in any case] stressors are neither chronic nor traumatic."
To say this would be ridiculous.
If what you mean is
Stress is normal unless it is excessive, and provided that the stressors are neither chronic nor traumatic
then you should use the version I suggested previously, with "or" AND NOT "NOR". If you insist on using "nor", be my guest; but you will not be making normal use of the language I have been speaking for many, many years, and that you claim to be interested in learning