Why Do I Get Chills All Over My Body?

when i play guitar with a friend i would get chills down my spine because how good it sounds, and another thing is when i like a part of a song i would get chills down my spine. or like at that doctor when the nurse or doctor checks my temperature, heart rate etc. i get chills whats the reason for that? the chills aren't painfull or anything they actually make me zone out into complete relaxation