I've had this happen to me several times within the last year. I'm not exactly sure why. Sometimes I just finished a dream and my mind was fully alert, capable of hearing all the conversations or sounds around me but i can't move. I can't even open my eyes, and when I try to speak no sound comes out. I've had cases where I can barely move my arms and have brought them to my face in an attempt to wake me up. Other times I am only able to just barely move my feet, trying to create movement to wake. And even though it has happened often, it makes me panic because each and every time I feel like it's something negative.
From the way you described it, there is nothing for you to worry. When you go to sleep, the body shuts down and puts you in a state of recovery. This is when the body heals itself and replenishes its energy. It is very common for people to become consciously awake while their body will then require some time to come back into function. In this time, the sensation of paralysis is very commonly experienced, and muscle weakness is not unheard of. There does not seem to be any reason for you to worry about it being something negative. In fact, I could probably say that if you are becoming more worried about this, then when you actually fall asleep, you are more likely to suffer from it again. Rest assured there is nothing standing on the edge of the shadows out to get you, and you should see a great decrease in these experiences.