How can you tell if the hemorrhoids is really serious?

You can tell! But...: ...are you sure you have just hemorrhoids? Pain +/- pruritis (itching) from the rectum that recurs may also indicate anal fissures, proctitis (due to infection, inflammatory bowel disease, radiation therapy, stercoral ulcers, rectal prolapse, trauma, etc.), prctalgia fugax. Depending on your age, risk factors, current medication (aspirin, nsaid's), circumstances, you will want to get evaluated.