Taking deep breaths after a big scare

Last week, I got a very scary and unexpected text from my older brother: he was being admitted to the hospital with a pulmonary embolism. I was flabbergasted: he's two years my senior, no prior significant medical history, healthy and fit as a horse.
He'd actually had chest pain for two days before it became unbearable. One car was in the shop, so he drove their minivan to the emergency room. He was desatting to the 70's on room air, and they admitted him with a suspected PE. Later, they confirmed multiple emboli and a pulmonary infarct.
I'm very grateful that he went to the emergency room when he did - otherwise, he may (probably) have died. But I'm really uncomfortable that there seems to be no cause behind the blood clots. He'll have further testing at his follow-up appointment, but for now, it seems to be unprovoked. That is so unusual.
Luckily, I deal with this scenario all the time - a patient discharged on blood thinners unexpectedly - and could determine which agent his insurance covered and apply a coupon to it. He lives in Minneapolis, but I called his closest Walgreens and befriended them to make sure he got superb care. I also spoke to his doctor, just to give my therapy recommendations, and he was very nice and concerned. It is somehow vaguely comforting that this is a common problem I see at work, and that there was something I could do: I think it's just human nature to want a role to play in an emergency; nothing is worse than feeling useless.
Meanwhile, my brother's poor wife was home with two babies (ages 1 and 2) and no car! She was a little panicked and not thinking clearly. I told her to call her church - they just moved recently, but what church wouldn't help in this situation? Sure enough, right away they sent a babysitter and someone to drive her to the hospital. It's so sweet when people reach out like this, and I know they were so appreciative!
My brother is home now, but as confused as I am (and exhausted. He's now at 3/4 lung function). We're hoping to know more after a more extensive workup, but for now we're just relieved that he is still alive!