As a self-published author, you have to go out and actively seek reviews if you want to get them. It takes a lot of work, maybe a little bit of deal-making, some letter-polishing and plenty of time. And if you can't take the criticism, you might as well not waste it...not yours, or mine.
You Asked For It
Before you actually ask someone to review your work, make sure you're prepared to hear it. Some authors absolutely want to get reviews for their books...provided those reviews are filled with praise. Others react quite poorly upon getting any sort of less positive feedback, and don't at all want to absorb criticism in any way.
There are a whole lot of reasons why you simply can't have this attitude. Even if you didn't ask the reviewer for a review specifically, even if it's just a random Amazon reviewer whom you can't track, you have to be prepared to absorb their comments in a healthy and productive way. The very second that you put your work out there for others to read, you're opening the door to criticism whether you go out and seek it or not. So whatever they say, you owe it to yourself to pay attention...no matter how painful it might be.
Time to Get Tough
If you haven't already had the sensitivity beaten out of you by the time you've decided to self-publish, I'm sorry. You're about to have some pretty ego-pounding experiences. Many indie authors have already been rejected, at least to their way of thinking, by the traditional publishing world. Agents and publishing houses are cold, impersonal, and their repeated rejections can hurt. More in-depth reviews are often even more painful, but at least those who have weathered rejection in the past have become a little more desensitized.
Either way, you've got to get tough and you've got to be objective. Anyone who ever reviews your work is a great help to you, no matter how cruel or hurtful their comments may seem. It's always extremely valuable to know what even one reader thinks, and every review is a window right into their thoughts. Any tiny piece of information they give you can be used to make your work better...even when it feels like they're ripping out your heart.
As a self-published author, you're exposing a part of yourself to the world and you're opening up a door right into your soul. That's the way it is. If you aren't tough enough to take all the slings and arrows that are coming, then please close the door. Don't let the criticism wear you down or diminish your love of writing. If you find that reviews are affecting you in a negative way, stop reading them. They can be a great help, but for some authors who are sensitive to it they can turn into a gigantic hindrance. You can still be a writer...just maybe a little bit more reclusive. And if you know you can't take it or you might be too sensitive to really process the criticism you receive, then stop asking for them. Any reviewer can get nasty if you manage to push the right button, and you never know when that might happen.
Whether you're reading the reviews or not, you have to be tough on yourself. Either be disciplined enough to ignore them, or be strong enough to really absorb them. For a self-published author, there really is no in-between.