It started about 18 months ago. I would get nasal speech as if I had some allergy. Since then I would have it occasionally, usually towards the evening. My speech would get extra nasal. Then it started more and more often, and now it is happening every day. I slur my words as if I am a deaf mute person and am hard to understand. All allergy tests are negative.. I start talking normally and couple of minutes later it s as if my vocal cords give up and I start talking like a deaf mute person, not being able to make some letters and sounds