Being a stay at home mom is like having any other job, plus being on call 24/7. You have daily tasks and responsibilities, on going projects, and deadlines. Though they may be different from what the average person may do on the job, they are still very real and very important. The only real difference is that you don't get paid for all of your work (with money that is. Smiles and giggles can be just as much payment some days.)
Every job I have had in the past has not been nearly as consuming as being a parent. That is obvious to anyone who knows anything about parenting. Most people don't have to live with their work, look at it every day, know that this particular project doesn't have an end date, and make sure that it doesn't talk back to them. That is, unless they are making robots, and in that case they want their work to talk back to them. Still, being stuck with your work bound to your side at all times can be a bit challenging. I have found that I lose who I am to all of the time that I am investing into the kid. I get to the point that I am defining myself by how good my kid is doing at meeting developmental goals, rather than trying to define myself as a being, separate from him. I become part of him, because I am like his needed appendage that takes care of all of his bodily functions. Without me he wouldn't have food, or be able to take care of his waste, or get around. He makes constant requests of me, and I respond like a third arm that just happens to be more skilled that the two that he actually owns.
This can be come a little depressing when I look at if from that perspective. So what do I do to alleviate that kind of internal struggle? I have a hobby. I take a little time during the day, like when he is napping or playing nicely on the floor by himself, to do something that makes me happy. Something that makes just me happy. Not just him or us, me. I take some time during the day to have a Me Party (http://www.youtube.com/watch?v=BXH3Gnvxpw0). I literally sing the song in my head while I am doing these activities.
My art and my writing and all of the up keep of these things I enjoy doing, have become my daily Me Party. Every one has hobbies outside of work. I don't think anybody is so one dimensional that all of what they are can be entirely summed up by what they do during work. Everyone I know has to have something outside of work to help them unwind, and give themselves more depth in life. Being a stay at home mom is no exception. I still feel it necessary to have hobbies, and do things that are not associated with being a mom. It has become my release for the day, and absolutely essential to keeping me sane.
It is okay to be selfish a little bit every day. I think everybody needs that kind of time to pursue things that they really care about, in order to stay sane and civil. No one should ever make you feel bad for having yourself a little Me Party every once in a while. If we didn't I am pretty sure all of us would be depressed and angry all of the time. Don't worry a little Me Party is healthy.