Federal regulators now want all train operators tested for Sleep Apnea, after a report this month found the engineer in September's deadly New Jersey train crash suffered from the disorder.
He was diagnosed after the crash.
The NTSB isn't saying that's what caused the engineer to slam his train into a platform, killing a woman, only that they are now considering it as a factor.
So that has a lot of people wondering, what is Sleep Apnea?
How do you know if you have it and what can be done about it?