personally i am a very large fan of permanent consequences in whump.. both mental and physical.. especially when it's literally transformation. oh whumper injected you with the SerumTM? you got cursed? you got used in a ritual? tough shit buddy, now your physical form is irreversibly and permanently changed, and you'll never be the same again.
i'm not sure which is better; whumpee being conscious and having to deal with the (usually painful) process and panicking and etc, or whumpee being unconscious and waking up in what is essentially a completely different body.. mmmm it's so good
hear me out- best of both worlds, a slow acting curse/consequence. you walk too long on a hairline fracture and it'll eventually splinter then compound. you ignore a pain in your side until you have to be rushed to the ER to remove your appendix. a chronic illness slowly ravaging your energy until you wake up and youre 30 unable to do what you could at 20. any fictional scenario could also apply to this. the Curse™ unfurling itself over the years, slowly constricting your life, patient but sure as sand in an hourglass. or perhaps the poison in the weapon-head that you had removed is now starting to travel to your bloodstream; one moment, you're celebrating your hard-won victory, the next you're vomiting blood. maybe you're a robotic/android whose body is degrading, the years making you little more than a bygone, with no repairs or replacements in sight; you can feel your fans whirring too loud, your memory chip degrading. you knew something was wrong, but you play it off because you're so sure you're fine, this is as bad as it gets anyways-- until the body you find yourself in is not your own, warped right beneath your own perception.