Relaxation: Meditation relaxes the body, both mentally and physically, but it is merely a by-product. Preksha Meditation involves a process of relaxing the body completely called Kayotsarga which needs the practitioner to be fully aware. It is an attempt to transcend the thought unlike many other common relaxation forms.
Thinking: Thoughts consume a lot of energy. Thoughts are responsible for emotional and mental turmoil creating stress. By transcending the thought activity, a practitioner realizes that he is not his thoughts. Casting off thoughts has several other benefits of increasing the vital force and will power.
Concentration: Meditation starts with concentration, but the ultimate aim is not to employ concentration. It is a tool to transcending beyond and reaching the ultimate goal of realizing the soul.
Self-hypnosis: Self-hypnosis involves concentrating but it does not involve staying aware or conscious of the practice. It is entering into a state of semi-consciousness which involves losing control of yourself. Meditation on the other hand, is being constantly aware and being in control of your doing.
Preksha Meditation is different from these techniques because it enriches one with bliss and peace, actually transforms a being to a happy and delighted soul. This is difficult to be achieved with thought or concentration.