Sleeping with your mouth open decreases your saliva production (Picture: Getty Images)When we sleep, our production of saliva lessens and only continues to decrease if you sleep with your mouth open or breathe through your mouth. ‘This paves the way to not only morning breath but also a bitter taste,’ Dr. Ahmed, from Viva Dental, says. This often leads to the lingering salty and metallic taste,’ Dr. Ahmed explains. A sinus infection can cause a salty or bloody taste in your mouth (Picture: Getty Images)What does a sour or metallic taste mean? ‘Brushing the tongue helps remove tongue coating (dead cells, debris, bacteria) shown to correlate strongly with bad morning taste,’ Dr. Ahmed adds.