Patients lie to their doctors constantly, and in some cases, it's understandable. You want to say that you work out 2-3 times a week when you only go to your adult dodgeball league once every two weeks. It makes you look better. I lied to my doctor in college in a much more nefarious way than simply exaggerating my self-care. I was on an acne medication that gave me all of the worst side effects I possibly could have, to the point where I should have probably been taken off the drug. However, I wanted beautiful skin and was willing to put up with two to three months of unwanted suicidal ideation to get that. I lied to my dermatologist about the side effects, and as a result, I haven't had more than two zits at a time for three years. In hindsight, I probably shouldn't have lied to my doctor because it could've gone horribly wrong, but at least the ends justified the means.
Often patients lie to their doctors for no reason but embarrassment. While doctors don't catch on to every lie, the ones they figure out can be hilarious.