Disadvantages of Immortality

Immortality certainly has its appeals. You have time to do all sorts of things, experience a lot of things. But what about the potential disadvantages? Things might turn out not to be as idealistic as you anticipated. Today, we'll explore some of the problems that could arise from immortality.

Disguising Age

"Wow, you're eighty years old? You don't look a day over twenty."

Obviously, that wouldn't work out well. People would begin to wonder about the strange person who's lived in town for many years, but shows no signs of aging. Perhaps they're one of the Fair Folk. Or maybe (gasp) they're a witch. Suddenly, the townspeople turn against this strange being, holding porches and titchforks, and the poor soul has to flee. Their home is aflame, they're being chased through the streets.

As a result, you'd have to find ways to disguise your true appearance. Makeup, masks, wigs... You probably have to go as far as disguising yourself as a nanny of the opposite gender, but nonetheless, it could be tricky.

Of course, there's also the option of moving frequently. Immortals have been using this tactic for centuries, or so the books, TV shows, and movies claim. Even then, you'd have to deal with the constant problem of having to create new birth certificates and other documents, lest someone wonder why the database believes you to be fifty years older than you look. And what if you've already gone to college for the job you're applying to, but you got your degree seventy-two years ago? It's a lot of work, pretending to be thirty instead of three hundred.
And what about making friends, or falling in love? You'd either have to hide the truth from them, or try to tell them the truth. They might not even believe it, or they wouldn't handle it well and distance themselves from you. You'd have to watch them grow old, or leave people behind as you live your nomadic lifestyle.

Sad and Lonely

Your family members have died. Your spouse is gone as well. You watched your children die from old age, and then your grandchildren. Friends die, and you make new friends. They grow old and die. It goes on and on. You even outlived your pet tortoise, and you're on your thirtieth generation of dogs.

Difficult to Relate to People

It's hard to explain to those young whippersnappers that you had to do everything by hand: beat rugs, make your own dresses. They don't know how good they have it, throwing their clothes in the electric dryer instead of putting them through the wringer. And here they are researching the Civil War for their history report, and you lived though the Civil War.
And really, no one can relate to being 250 years old. Nor are they the same generation as you, so they grew up with different interests, different experiences, different speech. Imagine growing up in the 1700s, and now everyone's using the slang of the 2000s. You'd have to be good at accepting change and adapting to new things, or you'll feel wildly out of place for sure.

Boredom, Bitterness

After watching a few centuries' worth of wars, natural disasters, and other tragedies, you grow tired of it. You've seen countless corrupt politicians, you've seen society make the same mistakes and sins without really learning from it. It's enough to make some people cynical after a while.

Besides that, what if you grew bored? The whole "do whatever you want" might grow old after awhile, or the value of mastering skills will seem cheapened to you. Some people would likely complain, "I'm four hundred years old, I've experienced everything. I'm bored with this!" And then they might do wild things, ridiculous things, awful things. 

Not Dying From Illness or Injury Turns Out to be Curse

Oh look, I lost my head! Literally.
Granted, if you had super healing abilities, this would be remedied. But what if growing a new body took a while? Or what if you were immortal, but didn't have inhuman regeneration like that? What happens then? Do you just sit around, a random disembodied head, for all eternity? Rather inconvenient, especially if your nose itches and you have no hand to scratch it with.

Don't mind me. I'm just sitting here, detached from my body, watching lions gnaw on my limbs and swallow my organs.

And what would happen if you fell overboard, but couldn't swim? You'd either have to figure out how to swim, or accept your new life at the bottom of the sea. Maybe you could walk until you found land. Though it might be hard without a map or any light to see by. What if you got caught in a landslide and were buried alive?
Sickness could be a problem, too. You'd have some sort of horrible malady (vaccines weren't really a thing hundreds upon hundreds of years ago), and be suffering terribly. You're feverish, delirious, can hardly breathe... Under normal circumstances, you'd be dead. But suppose you were alive despite being deathly ill. Would you just lapse into a coma for an insane length of time, until you finally recovered? Would it be possible to be too sick for recovery, despite immortality?
Let's go back to the whole 'swallowed in the sea' thing. What if breathing was a problem? Would you stay conscious without air, or would you be lying in the deepest depths of the sea, in a possibly eternal coma? Following this thread, how would things like hypothermia or heatstroke affect you? What about starvation and dehydration?
And what if you didn't go into a coma at all, but remained aware of your terrible hunger, or how the desert sands are burning you? What if you remained conscious, yet suffering terribly?

Aging Without Dying

You'd be blind, deaf, and have terrible arthritis. But hey, three hundred years old and and still kicking! Not literally, of course, you can't move much.
Similar to the problem of illness and injury, you have all these issues. If you didn't remain eternally youthful, you'll become frail and unable to do much. Your joints would grow stiffer, you'd be more prone to bone fractures, you'd have to invest in dentures. You lost the ability to taste much of anything about a hundred and ten years ago. Your skin is wrinkled as a prune, and you're more withered, perhaps, than any human being in history. The days of walking will be distant memories when you're four hundred years old, since that was over three hundred years ago.

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Indeed, there's plenty of potential problems. You could find yourself very unhappy a hundred years from now. The emotional strain might drive you to madness. You might get lost while exploring some caverns, a cave-in occurs, and you spend forty years trapped there. Think carefully before you accept that offer from the local sorcerer, or make that wish when the genie asks what you desire.