It sounds like whatever it is you are being asked to do is causing you significant anxiety. It sounds like what you are being asked to do is something you do not feel capable of doing. It sounds like you are desperately looking for an excuse to not do whatever is being asked of you.

To answer your question, yes. I have lied to get out of something. Usually when I do that, it's because I do not feel the other person will "hear" me. They'll hear the sound of my voice, but they will railroad over my insecurities and deficiencies and then I will be doing something that I know I cannot and should not do [because of my own issues.]

You say you feel devious, unreliable and lazy. That's a lot of hate to put on yourself. If you're not doing something you should do, then guilt is a common response and is telling you that you should do the right thing. However, if you are being pushed into doing something you absolutely do not/cannot do, then you should not feel guilty for saying "no thank you."