Going outside is overrated, right?
After all, you've got everything you need inside: food, water, working plumbing, and Netflix. If you wanted to, you could stay out of the sunlight for the rest of your life.
Of course, "the rest of your life" might not be very comfortable. Here's what would probably happen.
Your muscles wouldn't function as well and you'd lose bone mass.
You'd probably suffer from a vitamin D deficiency, so your body would have trouble using its muscles. Expect your normal aches and pains to become much less tolerable. If you've got an inflammatory condition like arthritis, you'll notice the difference pretty quickly.
A bigger long-term issue would be bone loss—vitamin D deficiency can cause rickets in young children and osteomalacia in adults.
Vitamin D is important enough that your body produces it on its own. However, we get about 90 to 95 percent of our vitamin D from sunlight, and while it doesn't take much sunlight to deliver a daily dose, this little experiment assumes that no light waves touch your skin, period.
That means that your bones would become increasingly fragile, so during one of your trips to the refrigerator, you might unexpectedly slip on a peanut shell (assuming that you're eating peanuts) and break your leg. That's definitely going to put a damper on the binge-watching.
By the way, you might want to skip the sweets. Since vitamin D aids bone growth, it's thought to reduce our risk of cavities.
You'd probably get sicker.
Some studies indicate that vitamin D plays a role in immune system functionality. Without enough vitamin D, you'll likely become more susceptible to certain illnesses.
Granted, you won't be going outside, so you might not get sick right away—until someone stops by to visit while fighting off the flu. Oh, and if you're not accepting visitors, the threat could come from your body; some research indicates that vitamin D helps to fight cancer and heart disease. There's even some evidence that vitamin D deficiencies contribute to the development of type II diabetes.
You'd get depressed.
According to the Mayo Clinic, serotonin levels drop off when your body doesn't have access to sunlight. That can cause seasonal affective disorder (S.A.D.), better known as seasonal depression.
Humans also evolved to sleep through the night and wake in the morning, and our brains produce a chemical called melatonin to regulate this process. If you don't have any access to sunlight, your melatonin levels will likely be abnormally high, meaning additional psychological issues. Since you won't be getting good sleep, those issues will likely compound over time.
Melatonin may also affect fertility, by the way, so if you want to have any kids, you might want to get that out of the way before you board up your windows.
With all of that in mind, maybe this isn't the best experiment. Go ahead and get a few minutes of sunlight (experts recommend at least 10 minutes of exposure in the midday, although you'll ideally use some sunscreen and stay outdoors for as long as possible). The couch will still be there when you get back.