What exactly happened to Don Elkins?

[YinYang]

I think Don was extremely positively polarised, Ra would not have made contact with a group if any of the entities in the trio were of negative polarity. You can also sense his polarisation in his questions, as least I can. Carla explains quite in depth what happened to Don in book 5, and it's important to remember that the contact was like a "blinding cynosure", as Carla described it, in terms of attracting negative attention. They were essentially under constant surveillance by the negatives, to find a way to end the contact. Don's doubts about Carla's love for him, and as Carla said "they didn't survive "three-ness", ultimately provided the opening the negative 5th density entity used to undermine the harmony in the group, and which led to Don's mental deterioration.

Don's alienation to Earth's vibration was significant, when him and Carla "switched" places, she experienced the terror he lived in for the first time. It's perhaps not the best thing to compare your personal experiences to the very unique conditions of the Ra contact, which was a potent magical working.

For me Don was always the one that got the wheel turning, and I shed many tears while reading book 5, it felt like a personal loss to me. His absolutely singular focus is commendable.