Light phenomenon identified as the tunnel to the Great Beyond
The great beyond was a Human concept of the afterlife.
In 2375, Julian Bashir and Miles O'Brien were incapacitated and near death while exploring a visual representation Luther Sloan's mind using Multitronic engrammatic interpreter technology. Unable to move and seeing a light appear in a certain imaginary corridor, O'Brien suggested it was the tunnel to the Great Beyond. This strengthened his resolve to continue, and they ignored the phenomenon. (DS9: "Extreme Measures")