Christopher Case was a 35-year-old music executive working for Muzak. In April 1991, Case experienced something that we can't fully explain, which cause him to die tragically.

On 11th of April, 1991, Case and a number of his collegues were on a business trip in San Francisco. During a dinner he and his collegues undertook, Case was introduced to a woman. According to Case, she looked ~20 years older than himself. Eventually, it became clear that Case and this woman had a lot of common interests. It also became clear that the woman was romantically interested in Case, while Case was not romantically interested in her. After the woman asked Case to come to her place numerous times, with Case declining each time, the woman declared herself to be a witch, and that she had put a curse on Case. Case was destined to die within a week. Sure enough, Case died 7 days later.

1. Some time in April 1991, Case and some of his collegues are in San Francisco, on a business trip.
2. On April 11, Case, during a dinner with his collegues, gets introduced to a woman. The woman takes a romantic interest in Case.
3. After Case declined the woman's request that the two of them go to her place numerous times, the woman declares herself to be a witch, and states that Case will die within a week.
4. The next day, Case is back in Seattle, WA. He calls his friend, Sammy, who's on the other side of the U.S., to tell her about this supposed "curse".
5. 48 hours after meeting the woman, Case, during the night, hears whispering in his apartment, and goes to investigate, thinking it's a burglar. Case finds no one.
6. The next day, Case calls Sammy again, to tell her about his experience the previous night.
7. That night, the same thing happens.
8. The following day, Case calls his other friends to tell them about the whispers.
9. On the 15th, after not being able to sleep for two whole days, Case finally does fall asleep. He wakes up a couple hours later, paralyzed. After some time, he hears the whispering again, first from another room, then from inside the closet, and then from under his bed. Finally, a black humanoid figure emerges from the foot of his bed, and picks Case up by the neck. When Case is about to pass out, the figure disappears, and Case falls back onto his bed. The next day, he wakes up with cuts on his fingertips, which caused his bed to get stained with his blood. He also notices handprints on his neck.
10. Case calls Sammy to tell her about this 'attack'.
11. Case then goes to a religious book store to buy books about witchcraft and demons. He also picks up a few crucifixes. Case then hangs the crucifixes around his apartment, and he pours salt along the base of his apartment's walls. In the corners, Case puts little salt piles.
12. On the night of the 16th, Case, for reasons unknown, goes, in the dead of night, to a hotel to sleep there.
13. The next day, Sammy calls Case's landline, only for him to not pick up. She calls the police and asks them to do a wellfare check on Case, but they can't get in, and Case doesn't answer the door.
14. After some time, Sammy notices a voicemail from Case where he states, in a defeated voice, that these things that are haunting him are going to kill him that night.
15. On the 18th, Case doesn't show up for work. This information finds its way to Sammy, who calls the police and asks them to do another wellfare check on Case. Upon arriving, the police find Case's apartment door unlocked. Upon entering the apartment, they notice the crucifixes and salt Case decorated his apartment with. They also notice scraps of paper containing messages handwritten by Case around the apartment. Case is found dead, in his bathtub. Case wasn't bathing, but just kneeling in his empty bathtub, slouched up against the wall, with his hands tucked against his chest. Case had no external injuries. The coroner determines Case died of a heart attack.

I, due to the tiny amount of information we have to work with, could come up with nothing more than a theory I'm ~78% sure in.

Anyway, here goes:
Case, likely while being at that dinner, consumed something that affected his brain in such a way that it caused him to develop hallucinations he believed to be actual, real things. Furthermore, as far as I'm aware, the coroner never reported that at least the remnants of the handprints on Case's neck, or the cuts on his fingertips existed. This leads me to the conclusion that the cause for Case's death was life-like hallucinations induced by something he consumed at the dinner, which then caused Case to die of fright. This, however, would only be possible if Case had some sort of medical condition that caused cardiomyopathy, such as diabetes, coronary heart disease, or even something simple as high blood pressure. I assume that he did actually have cardiomyopathy, since he reportedly took vitamin supplements daily, but that might have nothing to do with it.