d66/d18 Diseases

Picture of Dorian Gray/ Ivan Albright/ 1943-44.
For the 1945 film.

[Edit 21/06/2021 - Replaced table with nested numbered list; added pic]

A table of diseases for you to suffer; pre-supposes you're using something resembling Classic Six Ability Scores, but shouldn't be hard to convert and there's plenty of room for your own interpretations.

Use your own or someone else's sub-system for infection, incubation and recovery, because I haven't thought of my own just yet.

1st d6 (1 to 2) 2nd d6:

1. Cave Cough: otherwise indistinguishable from Island Cough until the first time you cough up blood. Fatal and caused by luminous microscopic shellfish native to the coasts, caves and dungeons of the Stranded Isles.
2. Crusticles: crumbly, scaly accumulations of calcium/keratin at inner joints, crotch, nose, mouth, corners of eyes; lose Dex and Str until bedridden, cure or recovery; if bedridden, it could kill you; very unsightly, leaves light scarring.
3. Dreaming Chills: lassitude, plummeting temperature, waking dreams, catatonia, false death, actual death. No known cure, but plenty of folk and quack treatments of varying efficacy that can delay or temporarily reverse progression. Considered quite attractive and romantic by some.
4. Fetters: Dex sapping, massive swelling of the neck, hands, wrists, feet, ankles, fingers, toes; shortness of breath, sluggishness, fever. Rarely fatal but attacks can flare up for years afterwards, especially when stressed or in hot, dry weather.
5. Fireseeds: masses of ruby red rice-grain sores all over the body and a scorching fever; only treatment is cooling until the disease burns itself out. Contagious, frightening and might cause SHC if you don’t have enough magical diseases. As an option, this disease can burn out another disease if you survive.
6. Galloping Rot: starts with a small infected wound, which can be treated with red hot irons; if exposed to sunlight, the victim decomposes within hours. Senses and mind are unaffected until final dissolution. Can be stalled by death and undeath.

1st d6 (3 to 4) 2nd d6:

1. Greasy Stinks: overproduce and exude fatty, oily substances; it smells so bad that you and those nearby are nauseated and dizzy; drains Con, but not fatal; temporary relief if sluiced with sufficient wine, vinegar or spirits; water has no effect; soap reacts to cause chemical burns.
2. Grey Waste: Pallor, lassitude, non-communication, hopelessness. Non-fatal, but the cause and cure are unknown. Temporary relief through eventually ineffective treatments. Sufferers seek the deep mists and solitude. Contagious.
3. Island Cough: really annoying, persistent cough - spoils spell casting, stealth and diplomacy; caused by exposure to microscopic shellfish native to the Stranded Isles. Normal remedies will treat the symptoms, but you need to leave the Stranded Isles to get it out of your system.
4. Laughing Pox: a bit like the Joker gas/poison and a bit like being Crossed; disfiguring boils swarm across the temples, jawline, chest and abdomen. Invariably fatal; those recovering will probably be executed for what they did, or take their own lives.
5. Phantom Epilepsy: a spiritual disease that affects the astral body, rendering the sufferer vulnerable to psychic attacks and unable to dream properly. Cannot be diagnosed by normal means, but tell-tale symptoms are feeling observed and threatening dreams.
6. Pseudovampirism: extreme reaction to alliums and sunlight, and a craving for iron-rich foods; induces creepy behaviour, stealthy movement and delusions of charisma. Con, Str and Wis loss in a race to the bottom, lying down to die in some dark, secret place.

1st d6 (5 to 6) 2nd d6:

1. Rat Fever: you don’t actually get this from rats, but everyone thinks you do and acts accordingly; fever, delirium, wasting, exhaustion; often fatal and very contagious.
2. Silent Disease: your mind and body waste away and you are unable to ask for help. Very likely a result of demonic possession.
3. Spring Gangrene: carried by ticks in lovely lush green places; the bites become smelly infected wounds. Easily treatable, but can lead to loss of affected parts and/or severe scarring if not.
4. Swine Blisters: unsightly with a debilitating fever; contracted from domestic and herd animals (including pack mules); usually attacks the hand webs, nostrils, lips and chin. Rarely serious, you can only have it once, and it vaccinates against one other disease (not necessarily on this list).
5. Wolf Head: very much like rabies, contracted from animal bites, but can be treated by conventional means; however, survivors are susceptible to attacks of lycanthropy (actual or delusional) in future.
6. Wrack: the most excruciating cramps you’ve ever had, all the time; limbs become twisted and rigid. Non-fatal of itself, but drains your Str to death as eventually you won’t be able to bear any movement or sensation, including eating and breathing. Usually drives you mad, too.

The Stranded Isles form the assumed/implied setting of my heartbreaker and most adventures I run, so that's what I tend to have in mind as background, but you don't really need to know anything about either to get use out of the table.

Maybe make the Swine Blisters vaccinate you from a disease against which a paladin's immunity is ineffective, so that paladins have a surprise vulnerability.

If you don't believe in vaccination IRL, then maybe you can suspend disbelief for a fantasy game.
By 'a bit like being Crossed' (Laughing Pox), I mean as in the Garth Ennis comic (it's pretty horrible, even if you like that sort of thing).