I will be honest and state that hypnotic regression was not the best evidence given to show any kind of abduction by aliens of people. Most of it can be said to be fantasy prone or dreams interpreted as reality. Until I read this book...
The Allagash abductions is a well known case about four young men who go on a camping trip and end up having a terrifying experience. The book, written by Raymond E Fowler, is a very well done book about the experiences and hypnotic regression sessions between the men. All four men give the most detailed accounts of what happened to them in this book. The graphic and undeniable detail makes this much more than a fantasy or dream. I do not know of any dream that can have so much minor and graphic detail in it.
All four men recount the same basic experience, and also draw illustrations as to what happened. Two of the men are very good artists and the details of the creatures are mind boggling. Also added in is the physical evidence given by the men of unexplained marks on their bodies.
Three of the men have accounts of being picked up earlier by the aliens and show multiple abductions. I was one to be skeptical of multiple abductions, but it would make sense if the creatures were studying humans the way biologists trap and tag wild animals.
After reading this book and the full unabridged accounts of what happened, one will want to sleep with the lights on for a while. A very well written and terrifying book. Highly recommended for anyone who wants to read about abductions. Skip the made up Hollywood movie out there now, and read the real deal.