My son lost his voice overnight with no other symptoms. he is 8yo. no pain no fever nothing. should i take him to the doc?

Time...: Laryngitis is often viral - if he is feeling fine, not having any other symptoms, and is able to swallow/breath normally then I would not head to the pediatrician just yet. Give it a few days to resolve (or seek care if other symptoms develop).

Allergies?: Try to have him rest his voice--difficult,gargle with salt water.It may pass.If new symptoms appear you may need to see a dr.--right now I dont think you need to.