This just might be a beta-endorphin increase in the male diver. Why not the female? I just don't know! I've learned many years ago not to predict what happens to ladies.
Anyway - here are some citations that show elevated endorphins in divers. It's not just pressure, either, as Dewey's second study showed little effect from a chamber dive.
Tripathi HL, Eastman NW, Brase DA, Dewey WL.
Effects of diving experience on submersion-induced increases in plasma levels of beta-endorphin in scuba divers.
Neuropeptides. 1991 Apr;18(4):223-7.
Tripathi HL, Eastman NW, Olson KG, Brase DA, Dewey WL.
Effects of hyperbaric simulation of scuba diving pressure on plasma beta-endorphin.
Pharmacol Biochem Behav. 1991 Jan;38(1):219-21.
Adams ML, Eastman NW, Tobin RP, Morris DL, Dewey WL.
Increased plasma beta-endorphin immunoreactivity in scuba divers after submersion.
Med Sci Sports Exerc. 1987 Apr;19(2):87-90.
Casti A, Orlandini G, Troglio MG, Bacciottini F, Michelini M, Maninetti L, Vezzani G, Rastelli G, Vescovi P.
Acute and chronic hyperbaric oxygen exposure in humans: effects on blood polyamines, adrenocorticotropin and beta-endorphin.
Acta Endocrinol (Copenh). 1993 Nov;129(5):436-41.
Here is the pertinent abstract:
Neuropeptides. 1991 Apr;18(4):223-7.
Effects of diving experience on submersion-induced increases in plasma levels of beta-endorphin in scuba divers.
Tripathi HL, Eastman NW, Brase DA, Dewey WL.
Department of Pharmacology and Toxicology, Medical College of Virginia Virginia Commonwealth University, Richmond 23298.
The submersion of eight male scuba divers in a state of neutral buoyancy for 20 min resulted in a significant increase (mean, 20%) in plasma beta-endorphin immunoreactivity (beta-EIR), and all subjects reported post-submersion feelings of well-being, relaxation or euphoria. The increase in beta-EIR was negatively correlated with age (r = -0.727) and diving experience (r = -0.860), and positively correlated with the amount of air usage during submersion (r = 0.863). Thus, diving experience appears to influence many of the nonsubjective parameters measured.