From the book that Kate posted, I understand the categories to be:
1 - Hypochondria. Being convinced you are ill when you are not. You do not have symptoms and it's entirely psychological.
2 - Facticious Disorder. You are a hypochondriac but have real symptoms that are psychosomatic. You are not ill but you really do feel pain/breathlessness/tachycardia.
3 - Munchausen's Syndrome. You actively harm yourself to induce symptoms. Often you are so deeply in denial about this that you genuinely don't think you're doing it, meaning it is a delusional/psychotic disorder.
4 - Malingering. You know you are not ill, but you pretend (with or without deliberately inflicting harm on yourself) for material gain, i.e. gofundme grifts, disability benefits. You are a fraud and you know it.
5 - Munchausen's by Proxy. You inflict harm on a dependent (usually but not always a child) in order to gain attention for yourself. You may or may not be so deep in denial about it that it becomes a delusion or psychosis.
There are also some guidelines for distinguishing among them. For example, malingerers typically aren't willing to do painful, invasive testing - they know it'll come up negative. In contrast, Munchausen's patients love being at the center of medical drama, so they'll welcome painful tests. (And if they come back negative, they can just say they have a rare and special condition - like
autistic frog chick Madeleine-Camille Preuninger, who describes herself as having "a strange history of having negative test results").
Another guideline: hypochondriacs are relieved when they're told they're not seriously ill, but they'll immediately start obsessing again and become convinced that they're sick. Munchies who get good news are disappointed.
That said, the cannier munchies read up on Munchausen's - I think there was someone in the first couple of hundred pages of this thread who claimed to be a recovered munchie and said she'd act reluctant to get tests so she wouldn't raise the doctors' suspicions, and some researchers have said that munchies admit to reading the research.
Normally the categories are described as mutually exclusive ... but I'm not so sure. For example, some munchies - Jacquie and Jonzie come to mind - get hooked on opiods, and in addition to playing hospital princess, they also turn into drug seekers - trying to get the material gain that's usually the defining characteristic of malingerers. Or look at
@choccy milk 's excellent
series on Heather Callahan-Williams - she always hung around cancer kids and seems to enjoy playing sick, but she also raked in at least $50,000 in donations.
I often find myself wondering which of these girls know they're faking.
Katie Stanina, for example, seems to genuinely think she's sick (and she does have epilepsy, but not MCAS, EDS, and all the other shit she claims). Some others definitely know they're not - which one of them said "I have a lot to do today before I get sick"?