As a professional and successful singer myself, I would tell you that my experience states that when your issues arises, you are not and should not sing. Put down the cigarettes, pick up the booze and lemon juice, and try again. If it continues, you shouldn't sing otherwise you risk breaking your vocal cords forever and will be unable to speak.
A fellow around here named Reynod unfortunately had this happen. He can only squeak when he speaks and if forced to only communicate by means of forums these days. They say he sounded like a sick angel when he used to sing. Now, God has forbidden his golden voice.