sudden dizzyness and weak through my whole body?

hi ,
i get sudden dizzyness and weak through my whole body its so bad i cant walk , this happens everyday and only relaxes for a while after lunch or a softdrink and i feel better 20 mins later and then symtoms come back again , ive had blood sugar test 5 times and they say its within normal range , i had to give up work ,i cant go anywhere in fear of getting weak and not being able to get home , 6 mnths ago i was an active strong confident 36 year old man and now im feeling like a doomed wreck with no answers ,i also get trembling and headaches when symtoms are at there worst , ive had chest xray,liver/kidney function /enzymes /full blood tests /thyroid function/and fasting glucose tests and all within normal range . im due to see a specialist in 4 weeks but feel i may not make it that long . any ideas would be appreciated ..thanks.......i also feel weird and i cant talk or think with any concentration and i sway slightly before symtoms get worse ..its very scary and a very very bad doomed feeling .......i dont get thirsty ...and iv always been thin ..6 ft 70kg
thanks