Well, I'm utterly sad to say that I've found out a lot more this week, and all the hopes I'd had of an underlying condition or accident have been crushed by the fact my mate deliberately took his own life in the MX-5 he loved.
As all I've read - he must have been in a terrible mental state (of which there was no sign) to have done this, but I think we'll never know why. He had (to us friends) a vibrant happy life, lots of wit, banter, travelling, good job, long term partner, an amazing house that they'd worked on for a couple of years. Don't believe there were money worries, and he was doing everything he loved even to his last weekend.
Something must have really got to him somehow, and I don't know why on that specific day. I do suspect work, but so sad given he was due a promotion the next day. Maybe something had gone terribly wrong and he couldn't see a way out without losing face / status.
Realising the fact that we'll probably never actually know why, but are gutted that he couldn't share with us how he was feeling, I wouldn't EVER think less of him for asking for help - I'd have been there. Still, he was always competitive & proud - maybe the trait of not lending himself to reaching out.
Sorry for such a post, we're all trying to find answers, which I think won't be found...
Dave