This is a big one, because I can see that people who used to know the difference between these two words have lost their grasp on it.
"Lose" and "loose."
To "lose" something is to come to be without it, to be deprived of it, or to fail to keep it; as in losing a job, losing a spouse, losing a wallet.
In the adjective form "loose" means unconfined or unattached, as in a loose dog, or a loose end. It's also the opposite of tight. My pants are loose, or at any rate they were earlier this summer. In the verb form "to loose" means to free from restraint, although it's a word not much used now. Mr. Burns from The Simpsons might order Wayland Smithers to "loose the hounds," instead of "release the hounds," although it's nowhere near as funny. (BTW, Google "Wayland Smith." You'll be amused.)
So, unless you mean that you are releasing your mind from restraint, you say "I am losing my mind," not "I am loosing my mind."
An easy way to remember it might be to keep in mind that you pronounce the two words differently when you speak them. "If I lose weight my clothes will be loose."
This lost/loose confusion has a meme-like quality, as I first saw it cropping up in the e-mails of otherwise well-informed folks about ten years ago, and now it's all over the damn internet.
It kinda makes me lose it.
