Mental stress is a noted contributing factor in chronic tension-type headache (CTH), however the mechanisms underlying this are not clearly understood. One proposition is that stress aggravates already increased pain sensitivity in CTH sufferers.
CATHCART, S., Winefield, A., Lushington, K., & Rolan, P. (2009). Effect of mental stress on cold pain in chronic tension-type headache sufferers. Journal of Headache and Pain, 10(5), 367-373. https://doi.org/10.1007/s10194-009-0131-5