I originally wrote this as a Supernatural fic but I think it works just as well here.
Unbeta'ed so any and all mistakes are my own.
Disclaimer: I do not own anything to do with Hawaii Five-0 other than seasons 1-3 on DVD.
It comes on slowly at first, creeping up on him like one of the many suspects he used to hunt before... Well, just before. He's not really sure when he started thinking of his life as having a 'before' and an 'after' but the memory of hearing his father being murdered over the phone seems to necessitate it.
Surprisingly, Mary is the first to notice; exhaustion has become the new normal and the ever-present bags under his eyes have morphed into holdalls that Vuitton would be proud of. He's surly and uncooperative, and downright refuses to acknowledge that it's not normal to still be tired after spending the afternoon passed out on the lanai, utterly oblivious to the racket being made by the seagulls further down the beach as they fight over scraps of food.
His voice goes next. It's Sunday morning and he tries to thank her as she places his coffee cup on the breakfast bar in front of him. It comes out as a high-pitched croak that causes Mary to raise a knowing eyebrow at him over the rim of her own steaming mug.
He breaks late Sunday evening, admits to something not being right and allows her to push him gently towards the stairs. He won't let her anywhere near him with the thermometer; The look he aims at it when she appears a few minutes later is enough to shatter glass and she's not willing to risk losing a limb trying to check his temperature.
The cough is a nice addition. She wakes to find his bed empty and the sheets are cool enough to suggest that he hasn't been there for a while. He's on the couch in the living room, not on the lanai where she expected to find him, with his face mashed into the back cushion and their mother's ratty old blanket pooled on the floor at his side. He starts awake, jumping upright when she goes to drape the blanket over him and his attempt at speech results in a coughing fit that leaves him slumped against the couch. He still manages to summon the strength to protest when she suggests seeing a doctor.
He loses the battle. Mary calls him in sick after the second sleepless night spent downstairs watching mind-numbing tv, patiently palms the back of his neck as he coughs and hacks for what seems like an eternity. "No," he manages to choke out and she squeezes his shoulder. "You don't have a choice," she says. He spends the afternoon being prodded and poked by a number of cold unsympathetic hands. He shivers as he sits bare-chested on the paper-covered exam table, not really paying attention as the elderly doctor explains that she's sending him for x-rays and blood tests to rule out pneumonia.
They're eventually sent on their way with a diagnosis of acute bronchitis and, much to Steve's displeasure, a shiny new inhaler.
He 'accidentally' leaves it sitting on the doctor's desk when he leaves.