How would you feel if you had cancer you didn't know you had. without knowing would you feel any different?

Why it's treacherous: Cancer usually does not affect the way you feel until it's gotten past being curable by local resection. This is why it's so important to go looking for it before you have symptoms. Best wishes.

Most cancers: Do not cause symptoms, particularly early. Therefore, you wouldn't feel any different until the cancer was large enough, or produced enough hormones or toxins, or was in a strategic place that induced symptoms.