Sub space, is when a submissive's body no longer feels pain but is in such a great state of arousal that they are "floating". It is different for everyone, but the generalities involved are the same. It can provide a connection that is almost psychic between the submissive and the dominant. It can totally relax the submissive. The physical arousal involved can cause orgasms of such strength that the submissive passes out. These physical and mental sensations can be a strong force behind desiring pain play. 

Dom-space is something that is still unclear. Some say it exsits, some say it doesn't. Those who say they have experienced it describe remarkebly similar feelings. They say they can feel a connection to the submissive where they can feel his/her breathing, see their movements even if they close their eyes, feel the arousal in the submissive, and their entire focus is on the submissive. The connection between to the two can be very instense, almost to the point of a trance. Many dominants speak of becoming one with their whip (or whatever toy they are using) where there movements are on pure instinct without conscious thought to drive them. Many also speak of a high state of both physical and mental arousal. These things are a strong driving force behing a dominant's desire to engage in pain play.

Another reason that many people desire pain play is the feeling of power that pervades the acitivty. The submissive (or bottom) can immediately feel the power the dominant has over them. Their own vulnerability becomes an aphrodisiac to them. This can create a major head rush for the submissive. By submitting one's body to pain play by a Top or dominant, one becomes intensely in touch with their own submission. They find themselves almost awed by the power the dominant has over them. Fear can play a part here as well. But it isn't a fear of the dominant, it is a fear of the unknown. Yet the unknown is sought and desired. The dominant can also feel power during such acitivites. They know that they can do what they want at that time and the submissive accepts it. They know that the submissive is willingly taking pain from them, and this excites a sadistic dominant. This power exchange in it's rawest form, is a mentally arousing thing.

Pain play is also an expression of trust from both involved. The submissive is giving their body to the dominant, for whatever he/she chooses to do. This a major sign of trust from the sub to the dominant. Trust that the dominant will not truly harm them. Trust that the dominant will make it enjoyable for the submissive as well, at least part of the time. Trust that the dominant knows what he/she is doing. Trust that the dominant will know when to stop, or honor a safeword if it is used. For the dominant, being able to inflict pain on a submissive and do so without permanent harm to the sub shows that they are worthy of the trust placed in them. 

Engaging in pain play activities, sometimes just for the sake of taking pain from a sadist without any sexual pleasure, can be an example of the love and comittment between the people involved. Not many people agree with this use of pain play, and some consider it abusing the submission given to the dominant. I, on the other hand, do not see it as such. I see giving myself to my dominant to use as he sees fit, as actually submitting to him. I take pleasure in knowing that my taking pain from him, provides him with pleasure. For me, and many others, submitting to pain play from a dominant, is a way of expressing how much we care about the dominant. A way of telling him/her that we care so deeply that we are willing to give them our bodies freely. 

I enjoy pain play for all of the above reasons. You may enjoy pain play for a different reason, and that is okay. Enjoying pain play, is not something to be ashamed of because most likely the reasons are perfectly understandable.