This is a classic, classic, thread! First off, the dude starts by saying everything he's talking about is from 2nd hand info. So right away you all should know to take it with a nicely sized grain of salt.
That being said, both stories about his 'friends' are quite silly indeed. The chap who saw shit after lifting heavy objects was merely suffering from low blood pressure (i.e. not enough oxygen getting to his brain for a few moments). You don't need to have ever injested a psychoactive compound to experience this type of 'flashback'.
As for the 2nd person, I don't know quite as much about the energy/light spectrum but certainly seeing innaproriate colors is quite commonplace. Light is weird light that, images can stay on one's retina for longer than desired times, and the mind can do some rather confusing things with light and breaking it down.
hope some of this helped...basically, nothing in this thread has anything to do with flashbacks (which do exist, but aren't worth getting into here, just use the search button or read up on google).