Numbness in right arm today. Feels like it's in the muscles?

No feeling. Numbness should be the lack of sensation - you can't tell if water is hot or cold, can't tell texture of cloth or the type of coin you are holding. Sensations in the muscles are tingling or pain, and these sensations can have many causes, from pinched nerves in the neck or arm, to tiredness or strain of the muscles. If it doesn't go away in a week or two, have a physician examine you.