There are some perfectly good definitions in Google and Wikipedia, and the people who've contributed to them are probably smarter than any one of us.
Cults are about control. They're about power, and the beliefs aren't the main thing - they're excuses.
It may be simplistic, but I tend to look at what happens to people who question, or what happens to people who leave, or try to.

...and if sleep deprivation is a sign that an organization is a cult, consider every military's basic training (that I'm aware of). But you can ask questions, and you can leave.