Awake mind after meditation

Recently I have started meditating on my own, by observing my breath and rise and fall of abdomen. Half an hour in the morning and half an hour in the night before going to sleep. Sometimes sleep takes over and I go to sleep immediately after meditation. But when I try to concentrate more during meditation, my mind becomes charged and even when I sleep, my mind is awake , although body is resting. I aware that my mind has not shutdown. Is this normal? am I doing correctly? This wakefulness is there till next day. Is this some kind of alpha state of mind? Please help.