First of all, see a psychologist and a psychiatrist. That level of suffering has to be dealt with the help of people whose expertise is to help people with mental suffering.
If you have that part covered I can share some of my experience that may apply to you. I've dealt with mental health problems all my adult life. I'm much better now. I have learned some things along the way.
I've learned to deal with my problems mainly with two strategies. One of them is to do metta for myself. Metta means loving kindness. It is a form of meditation where you arouse feelings of loving kindness (either to your self, or to a dear relative, etc.). A good guide can be found here: http://www.buddhanet.net/metta_b.htm
. This is very important. Low self esteem problems can be handled very skilfuly with loving kindness towards yourself.
The other strategy is by practicing mindfulness. You have to be relatively stable to practice either of the forms of meditation. And even then you should aproach it gradualy. But cuting to the chase, your goal is to clearly comprehend that the fear you feel is unjustified. What I mean is that you attribute more importance to the fear you have, than the importance it actualy has. Fear has a function, from the evolution point of view. It enables you to avoid risks that might get you injured or killed. But we are humans. Independent humans in a civilised society. Fear has almost no function anymore. It's an unjustified emotion. It only makes you suffer because you think it's justified. You think it's a valid emotion that you should care about. That you should act acording to that fear. In reality, that's not true.
The Buddha explained that the cause of suffering is attachment, aversion and ignorance. Fear is a form of aversion. Ask yourself: have you ever really benefited from the fear you have? Meaning: you obviously prefer not to feel pain, or to get sick. But you can act to do that without fear. Fear is useless. Its importance is completely unjustified. Have you ever benefited from fear in a way that you wouldn't just with the preference for well being, that is natural to all humans? How much suffering has fear brought you? I bet a gigantic amount. How much happiness? I doubt there's any. The advantage of trying to see this for yourself far outweighs the disadvantages.
Regarding your voice. I heard a teaching, not too long ago, by the great monk Ajahn Chah. When people would go for him to ask for help with their suffering he would often reply: "what are you attached to?" That's what it boils down to. You had a taste of what it's like for you to speak with a clear voice. It must have felt very, very good. Now that you don't seem to be able to do it, you are suffering. You are attached to speaking with a clear voice. It's perfectly understandable that you feel that way. But the attachment to that experience will only lead to suffering. It doesn't mean that you lose preference for speaking with a clear voice. It just means that attachment is not helping you feel better. Just let go of that attachment as if you were relaxing a muscle.EDIT:
I forgot to add something important. I don't mean to say that you should not feel fear. You do, and you will, feel fear. What I mean is that, if you understand that that emotion is completely blown out of proportion, that you give much more importance than it really has, then you will feel fear, but in a very different way. It reminds me of a story told by a tibetan master once: he was talking about how a group of tibetan refugees went to the movies for the first time. They had never, ever seen any TV before. So, for example, when it started to rain in the movie, they tried to protect themselves from the rain. He compared this behaviour with our human behaviour towards experience. Not to get technical, people attribute importance to emotions and views that they don't really have. And what has been my understanding of this analogy so far is that I now feel fear, but I don't care much. It's a sensation in the body. An unpleasant one. But it's no longer debilitating.
I hope this helps.
Again, this has to be done while being followed by mental health professionals.
He turns his mind away from those phenomena, and having done so, inclines his mind to the property of deathlessness: 'This is peace, this is exquisite — the resolution of all fabrications; the relinquishment of all acquisitions; the ending of craving; dispassion; cessation; Unbinding.'
(Jhana Sutta - Thanissaro Bhikkhu translation)