Of late, I've been slacking terribly with my practice. I sit at the piano, but can't seem to concentrate properly, and my hands seem somewhat slow. I just can't seem to focus. Have you ever gotten into anything like this, and how did you break out of it?

Any suggestions will be very much appreciated!

Ahhhh been there many times. It seems to always come down to a couple of things: THE MUSIC I AM STUDYING. At times I have had to accept the fact that the piece of music I am practicing IS NOT FOR ME or else is boreing me to death and holds no interest what so ever for me now or in the future!
Second thing: PHYSICAL and MENTAL STATE OF BEING: When I am over worked, stressed, tired and have anxiety I do not practice at all well. Also, diet and sleep seem to effect my ability to practice.
Of course the main question: FOR WHAT REASONS ARE YOU PRACTICING : To please someone other than yourself, an upcoming performance, competition deadline, or the joy of self discovery? WHY?
Goals and dead lines drive me into praciticing more than anything! LOL.

I'm always in that state. How do you break out of it? you wake up one day and realize your deadline is right on top of you and you have pushed your procrastination way beyond it's maximum limit.

Definately due to mental state (assuming you used to practice well, and you want to practice well).

That happened to me this past winter.

Probably because:
1) Senior year of HS
2) Graduation and going off to college next year
3) College applications
4) College auditions
5) Competitions
6) Winter = cold and dark
7) Family illnesses/depressions
8) A.P. Calculus
9) Recitals

As soon as 3-6 were completely over with, suddenly I became able to practice a lot more, a lot better, and I am shocked at the improvement that I have been making.

All of the rest will soon be over with as well, except for maybe #7...

Auda, this happens to me as well. One of the things that helps me is trying to pick ONE particular thing that I want to accomplish with one piece. Often I mess up my concentration because I'm thinking too much about my entire workload, and not enough about manageable parts. Example, sit down at the piano and warm up, then decide which piece to work on, and for how long. (a half an hour works well for me. it's easily doable, but still enough time to get a few things done) Pick a phrase or section, and decide on one particular thing you want to accomplish with it. Then just work on it. If you get it how you want it, pick a different phrase or section and do the same thing. Breaking up your time/tasks can be a big help and make things much less overwhelming. Regards!

Try the following, maybe?
1. do shorter practice sessions
2. try to accomplish 1-2 goals instead a bounch
3. slow practice
4. take a break till you feel you can't wait to go back to practice
5. learn something new
6. harmoically analys your piece
7. listen to some others playing the piece, draw new inspirations

Thanks for the suggestions you have given me. I will try some, and see how it goes.