My Theory (spoilers)
The bride hung herself on her wedding night. This probably happened in the 50s. Decades later, probably 90s or 2000s- the old man who checks in. He is the groom, decades after the suicide. He plans out - and successfully -kills himself in the room where they originally check in- by slitting his wrists in the bath tub.
Claire (possibly sensitive to ghosts) witnesses this- And is then haunted by the bride and groom. She is then scared to death (asthma).
What did I miss/ get wrong ?