What meditation practice will allow me to sleep less and focus more?

I have an issue picking meditation to practice during my free time as a medical student. My free time is limited and my stress levels are sky high. What is the best meditation practice for me out there? something that will keep me awake as well as improve my power of focus. My attention deficit is creating huge problems in my studies. --- Thanks you guys... the 1st answer is the most comprehensive. I do remember when I was a teenager I used to practice Metta mediation and had a better time falling asleep. But as I became a medical student and am currently studying in my 3rd year, my mind got clogged with the ever increasing amount of knowledge and stress, that I felt like I was trapped in this dogma of man made knowledge and lost all the freedom I had as kid. But I feel now, that that freedom I lost is actually mostly because I lost my path as a meditator and a Buddhist practitioner more than anything else. I should find the time to do these little things, because they are those little things that makes us complete. Thanks so much for the responses!