Well the critical question is are you stressed?

It's not the environment per se, but how you react to it.

I was on the phone with my co-worker who died of an embolism multiple times the day he died and was on a webex listening to him present when his line went silent before he passed.

He would have said he was handling the stress fine.

I’m not sure if this is normal and just happens to people - it just seems like an awfully high percentage of people.

Well stress is a killer.

Hypertension can be a major risk factor. Whether the person "feels" stressed or not.
Is your blood pressure normal/under control?

x2. The brain is the most powerful organ in the body.

Good grief....that is horrible. I am sorry for you.
Work stress can be perceived by the person or not. Wonder what his BP, cholesterol, activity level was before his death. Was this completely out of the blue or did he know about underlying issues? If you have cardiovascular issues, high BP, high cholesterol then the stress of a job can definitely through you over the edge. If you are healthy, with good outlets, support at home then not so much.

How many coworkers do you have? How many has something catastrophic or disabling happened to? What type of job is it?

Pretty much impossible to tell in individual cases (with such small numbers, there's no way of knowing if these cases were coincidence or causally related to the work environment). The only thing you can do is to look at a large number of people in similar circumstances to see if there is a statistically significant risk associated with the occupation.
Just like with smokers and lung cancer: you will never be able to prove that an individual's lung cancer has actually been caused by their smoking habit (a person might have developed the cancer even if they had never smoked), but if you look at large numbers of smokers and compare them to non-smokers, there's a clear and undeniable link between smoking and a strongly increased risk of developing lung cancer.

I’m not a doctor but here goes...

I think it is stress related but not necessarily the “stress” itself.

A lot people who are under stress drink a lot, eat like shit and don’t move around much.

Others who are under stress go run, do kickboxing or yoga and manage to eat a relatively healthy diet.

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Civilize the mind, but make savage the body.

- Chinese proverb

I've had one co-workers who committed suicide. Just didn't show up one day. Super nice guy - when I had started he'd gone out of his way to make sure I was invited to all the social things, invited me to his lunch circle, etc. I don't know why. I asked our boss, and he opened his mouth about to say something, then decided not to. So he probably knew something.

Another was an older admin. One day she asked me to drive her home because she was having some vision problems. A few days later she was dead from diabetes. Which I thought was really weird and sad given we all had really great health insurance. She must have just been working really hard to ignore the signs. And she was weeks from retirement.