Meditation notes

I previously tried to set up a meditation routine by trying out a 30 day meditation experiment.
During this period, I was having difficulty centering my mind. I would also have frequent headaches, I would feel very sleepy during the meditations, etc. So I had to stop the experiment after a week.
Recently, what's happening is that I do meditations spontaneously. Whenever I feel calm and relaxed, I just sit down and let go, and usually after 15 minutes, I get a little restless and then I open my eyes.
It's a paradox that meditation is supposed to calm your mind but to meditate effectively you need a calm mind to begin with.
So what's helping me is to do shavasana before meditation. Shavasana or corpse posture in yoga is well known technique for completely relaxing the body. Once your body is relaxed, you can observe your mind easily during meditation.