So without benefit of typing symptoms into WebMD, here goes.
#1) "Her flashing eyes" -- Could be conjunctivitis, bilateral cataracts, or retinoblastoma (RB). Forget that RB is typically fatal by age 5 if untreated and your character is 25. We're not dealing in 100% reality with this romance novel thing anyway, are we?
#2) "His heart beat a tattoo against his chest" -- Clearly this description represents atrial fibrillation with rapid ventricular response. Give IV cardizem and if that fails, push amiodarone. FYI, expect to personally drop a load when you give amidarone. This med causes a prolonged pause in the heart where the person looks, well, dead, as they can be pulseless for several seconds until the heart rhythm resets and "jump-starts." (hopefully restarts)
#3) "Moisture pooled" (female) -- Uh, gonorrhea, maybe? Can I have more details? Does the moisture smell like dead fish or is it neon green? Ok, if not, then answer me this: is she pregnant? Because rupture of membranes might not be good. Finally, is she a "more mature" heroine? Consider OAB (overactive bladder). How to treat? Well, that Depends…
#4) "Loins tightened"/"bulging loins" (male) -- See reference to gonorrhea above. Inguinal lymphadenopathy, anyone? How about let's raise some awareness for testicular cancer. Anything resembling a mass needs to be evaluated, pronto, and not by the heroine's "tentative, gentle, probing fingers". Come on, she's not a trained professional, unless of course your heroine just so happens to be a urologist. In that case, game on with the probing. If it's part of foreplay, I believe your insurance cannot be charged the medical fee.
#5) "His essence tasted sweet" -- I'm going with diabetes on this one.
#6) "Her essence tasted sweet" -- Yup, yeast infection. Or flavored lubricant. Use clinical judgement.
#7) "A muscle jumped in his jaw" -- Is your burly hero up to date on his tetanus booster? Has he had an encounter with rusty metal or plant materials (sliced by a medieval blade or running through the woods to escape the bad guys)? If you don't get him tetanus immunoglobulin, every muscle in his body, including the diaphragm, will go into spasm and he will die. Awake. Suffocating to death. Opisthotonic. Don't do that to your hero. It's a rotten way to die.
#8) "Her mouth went dry" -- Uh oh. Let's talk xerostomia (pathologically dry mouth). Normally attributed to medications or illicit drug use or salivary gland tumors. Review medication list, perform urine tox screen, or CT the head and neck -- whichever is appropriate to the situation.
#9) "His gut clenched" -- Good grief, this guy's gonna die. Differential includes appendicitis, Crohn's disease, pancreatic cancer, irritable bowel syndrome, colon cancer, exploding prostate, and flatulence, to name a few items. Comprehensive testing is in order.
#10) "Her breath caught" -- Well, dammit, can't anyone remember ABC's of resuscitation? Airway, breathing, circulation. Sounds like mouth-to-mouth (no tongue please, we're professionals here) is a good start. Check for foreign body (again, not with your tongue, dude). Is she allergic? Did she eat a peanut and has anaphylaxis? This calls for emergency medical care with a shot of epi STAT.
Bonus condition "Even though they had just had rapturous, earth-shattering sex for the past several hours, he found himself hard for her again." Ok, let's have a frank talk about priapism. It's not just a funny-sounding word. It's a medical emergency. Nothing kills the mood faster than having to drain the dorsal vein of the penis with a 22 gauge 1 1/2 inch needle. Or so I've heard. (Didn't hurt me one bit.) :)
Legal disclaimer: None of the information contained herein is intended for use by the untrained author to treat or diagnose their characters' medical conditions. For characters' persistent or life-threatening conditions, please consult an editor for further assistance. If I can save the life (or reproductive organs) of just one fictional character, then this work has been worth it.