Weight loss and constipation. Will be referred for a colonoscopy soon. Should I be worried?

Hi.I'm 78 years old and  I have suddenly lost 5 kilos in as many months without trying and have developed constipation.  I went from 77.5 kilos to 72.5 kilos
 
I have had a full blood test including urine and faeces and my doctor says everything is fine but he has suggested a colonoscopy.  I have to see the doctor at my local hospital for a checkup on Wednesday and then he will give me a date for the colonoscopy.

Having done some research on the internet I am now extremely concerned that I may have colon cancer.

Should I be concerned.