For this, I wouldn't recommend a doctor, but I would say that your nightmare is the cause. You probably just had a really bad dream and you maybe moved alot in your sleep, maybe flailing your arms? But this could cause tiredness in the limbs and not highly neccesary for a doctor, if it continues however, maybe you should go to the doc just to be on the safe side if you were freaked out that much.
Maybe you just slept so deeply that you caused prolonged pressure on a nerve which caused the temporary numbness.
You should go and see a doctor, because arm numbness may be a symptom of a an underlying disorder or condition: There are many other reasons for discomfort in your arms which are not necessarily connected to sleep, e.g. pressure on periphere nerves (carpal tunnel syndrome, sulcus ulnaris syndrome, Loge-de-Guyon syndrome...), circulatory disturbances, problems associated to cervical discs in your neck area or spine in general (spondylosis, moving discs, trapped nerve syndrome). Some systemic neurological disorders may also cause arm numbness, such as multiple sclerosis and systemic lupus erythematodes.
Hope you are feeling better soon.
wow, way to go! way to scare somebody.....
Welcome to the MedHelp forum!
The weakness in arms can be a panic attack due to the nightmare. It can also be due to a pinched cervical spinal nerve due to wrong posture while sleeping. Other than this it can be a mild mini-stroke. Arm numbness can also be due to poor circulation which happens if the arms are compressed under the body while sleeping or kept in a particular position for long.
However, since you remember having a nightmare, I would think more in favor of a panic attack, with probably a cervical spinal nerve compression.
It wouldn't hurt to consult a doctor and rule out high blood pressure, and get yourself examined for other factors associated with ministroke.