Performance anxiety is very common and easily treatable. One of the things that is at the core of performance anxiety is that "I must be perfect all the time" this thoughts adds lot of anxiety. This anxiety contributes to your mistakes and you negative belief gets strengthens.

Tremors, feeling anxious or nervous, sense of panic, sweating, increased heartbeat, feeling of impending doom, stomach discomfort, dizziness etc are signs of anxiety. These can be debilitating. If the anxiety us overwhelming, consult a psychiatrist at the earliest. With the right medication and counseling, it is likely your symptoms will improve. Other than that, try yoga, deep breathing, meditation, moderate exercise, progressive muscular relaxation and guided meditation.

It natural even for a professional speaker dear. It is now you are yourself that let it sweat still I will complete my presentation , is what the  challenge you set for yourself, which would help you to ha dle and face the situation like that.

Hi u seems to suffer from social phobia but you need to get further detailed evaluation for your anxiety symptoms and also whether any depressive, sleep disturbance any emotional turmoil or believes which troubling u. A combination of medication and psychotherapy can help you in your situation.  Also please get your blood pressure checked for 2 to 3 days and look for its reading. Thanks