In the USA, if you achieve a USCF rating of 2200 and gain the National Master title, what happens if your rating then goes below 2200? Is the "National Master" title awarded for your entire life? Or do you lose the title if your rating goes below 2200?

I've heard that to get the title of National Master for your entire life you have to have a rating of at least 2200 for 300 games (that seems to be a lot!). Is this true? And is it 300 consecutive games (if your rating goes below 2200 before the 300th game you'll have to restart from the beginning) or simply 300 games not necessarily consecutively (it doesn't matter if your rating goes below 2200 a few times) ?

Oh and what about the FIDE titles "Candidate Master" and "FIDE Master"? Are they awarded for life?
There are actually three different distinctions in the USCF system that have to do with a 2200 rating.

First is the National Master title. It is awarded to anyone who has ever had an established (not provisional) rating of over 2200. Once a player is a National Master, they have the title for life no matter what happens to their rating. The NM title has no effect on rating floor other than the 2000 floor which a player receives for having crossed 2200.

The second and third are both called Life Master, confusingly enough. To distinguish between them, they are usually referred to as Life Master and Original Life Master.

Life Master is part of the norms system which was introduced in 2008. To gain the title, one has to have 5 performances in USCF tournaments that qualify for "M" norms and have achieved an established rating over 2200. To see a player's norm history, click on the link next to "Highest USCF Norms-Based Title Earned (in events since 1991)" on their member page then click on Norms History. This title also has no extra effect on rating floor.

Original Life Master has been around for a long time. It is achieved by starting 300 games (not necessarily consecutively, as far as I know) with a rating above 2200. Once a player has started the 300th game, they are given a lifetime floor of 2200. To my knowledge, this is the only way to get the 2200 floor-2300 gives you a 2100 floor but 2400 does not raise it.

Candidate Master is a FIDE title awarded when you make 2200. FIDE Master is at 2300. They are both awarded for life.

Edit: For reasonable evidence that the 300 games do not need to be consecutive, see the rating history of USCF member ID 12462971.