What Causes Weakness?

hi doctor , i am 46 year old male from India, i walk approx 5km every day . my total cholestrol is 147 mg/dl, hdl 45 ,ldl 84 , triglicerides 89 vldl 18. ratio Tchol:/hdl 3.26. my fasting sugar is 72 and post parandial is 104mg/dl my serum creatinine is 1.34mg/dl. i have 14.2% hemoglobin., some times i feel weak suddenly ,which lasts for 4to 5 hours. what should i need to do ? i feel as if my legs are floating at that time. pl help me , it is making me panic. my job involves lot of travelling, but now to travel it makes me jittery , due to weakness. thanking you bhargava