Physiologically, sleep paralysis is closely related to the paralysis that occurs as a natural part of REM (rapid eye movement) sleep, which is known as REM atonia. Sleep paralysis occurs when the brain awakes from a REM state, but the body paralysis persists. This leaves the person fully conscious, but unable to move. The paralysis can last from several seconds to several minutes "after which the individual may experience panic symptoms and the realization that the distorted perceptions were false".[5] As the correlation with REM sleep suggests, the paralysis is not entirely complete; use of EOG traces shows that eye movement can be instigated during such episodes.[6] When there is an absence of narcolepsy, sleep paralysis is referred to as isolated sleep paralysis (ISP).[7]

In addition, the paralysis state may be accompanied by terrifying hallucinations (hypnopompic or hypnagogic) and an acute sense of danger.[8] Sleep paralysis is particularly frightening to the individual because of the vividness of such hallucinations.[7] The hallucinatory element to sleep paralysis makes it even more likely that someone will interpret the experience as a dream, since completely fanciful, or dream-like, objects may appear in the room alongside one's normal vision. Some scientists have proposed this condition as an explanation for alien abductions and ghostly encounters.[9] A study by Susan Blackmore and Marcus Cox (the Blackmore-Cox study) of the University of the West of England supports the suggestion that reports of alien abductions are related to sleep paralysis rather than to temporal lobe lability.[10]

Many perceptions associated with sleep paralysis (visceral buzzing, loud sounds, adrenal mental state, presences, and the paralysis itself) also constitute a common phase in the early progression of episodes referred to as out of body experiences.[15][16] Mental focus varies between the two conditions; paralysis sufferers tend to fixate on reestablishing operation of the body, whereas subjects of out-of-body episodes are more occupied by perceived non-equivalence with the body.

Barbie,

You said you saw your mum on the stairs and she saw you. Have you spoken to her to ask if she did see anything strange on the stairs?

From what you're explaining, it does sound like an OBE to me. It sounds very similar to some experiences I've had. I've not experienced much, as I only practiced it for a little while but I did have 3 experiences but they only lasted a few seconds each; however, a few days ago I too decided to start practicing again.

I've got some interesting radio interviews and documentaries on my YouTube channel regarding this topic and you may find them interesting if you haven't already heard or seen them.
http://www.youtube.com/user/dukeselwood