Hello,
It sounds like you are doing what is referred to as "lucid dreaming." This means you are aware that you are dreaming. When one is in this state their consciousness is quite "fluid." This means that the ego centered focus has relaxed and the idea of "form" is no longer used as a means of identity.
When one realizes they are dreaming, they immediately are "out of body." With this change in focus one can literally become anything....a rock...a tree....a tiger. This tiger you come in contact with is a part of you and you a part of it. You are exploring another aspect of yourself. This part of you (the tiger) has things to teach you. This is magic in its purist form.
There are many great people who have become familiar with dreams and the mobility of that state of consciousness. Edgar Cayse is one example. If you "google" that name you could learn a lot. Another one to check out is Robert Monroe. He is known for the out of body experience.
You are involved in a magical thing here and you can learn a great deal through this. It is important to relax and refrain from being concerned about your corporal existence and flow with the shape shifting. This is "big" magic my friend....go with it.
I believe you have given yourself a gift and you can utilize this to your advantage and learning experience.
With Kind Regards,
Daniel