Jeez, I'm biting my fingernails again!

Help! It started this week. I noticed that I started biting my fingernails again. I haven't done that since I was about 17. OK, that's not exactly true. In my late teens I made a deal with myself; I could only bite the nails on my thumbs. It worked! The nails on my fingers looked great, my thumbs not so much. In my late twenties I decided it was time to stop biting the thumb on my right hand (don't ask me why it was the right). For many years I only nibbled on the left thumb nail. I did it unconciously, when I was working or reading mostly. Then, for some reason about 4 years ago I stopped completely. I think I was just too tired, too busy or both. I'm not going to tell you how many years it took in all, but I slowly trained myself not to do it!! Now, this week I've noticed lefty looked short and a little ragged again. WTF? Now the right thumb nail looks a little worse for wear today. I'm not sure if it's stress, excitement, anxiety or what but hopefully I can get it under control before I lapse back into that very bad habit. I have enough other ones!