It most likely means that you’re tired. Often when people attend retreats they realise how tired they are. Sleep is very important so honour the body. On the other hand, be aware that the mind is a tricky thing so it might be using sleep to avoid doing the mind training. Pick a time for mind training when it is less likely that you’ll fall asleep, and don’t be too warm or too cosy. Be curious around how the sleepiness is experienced in your body.
Being mindful is opposite to being distracted. In dealing with pain we follow Rumi’s advice: “The healing of the pain is the pain.” In other words, we enter into the body sensation of the discomfort and we keep following it till we really sense it, and then we just stay with it, breathing with and in it.
There is both formal practice and informal practice. The informal you can integrate into your daily life, like being aware of the breath and following the breath for five breaths every hour. You can start your formal practice with 10 minutes of mind training a day. You can begin with a basic meditation called ABCD.