I'm a hikikomori, and have been for almost 25 years now. It definitely is a syndrome which stands onto itself, it is a separate thing which you might catch under social anxiety and such, but it really is and should be a separate diagnosis.

In the first years your loneliness and isolation are unbearable. Then, years on, the unacceptable gradually becomes the norm. Then, slowy, after many years, you start to outgrow it and become a more voluntary hermit.

For me, childhood abuse on many levels and years of being bullied without mercy have brought it on for the most part. Hikikomori isn't autism, not even close. Autists (bless them) are born different, Hikikomori however are made (or rather: broken) by outside influences.

Autists are different by their nature and thus will forever be autistic, but can learn to cope. Hikikomori have the blessing that they can heal, but have the curse that they were broken, shattered to pieces from the whole person they once were.

If there are any fellow Hikikomori out here: bless you. Be true to your nature, and try to have faith that one day life will feel good again. Do not let yourself be forced too much by the outside world, but also do not get too comfortable in the cocoon you live in.

Be yourself, and be true to yourself. Like most hikikomori you will probably in several months or years overcome this, and if you do not succeed, you will eventually overcome the despair and pain itself.

Know that somewhere in that frightening, threatening outside world, there on a safe distance is a fellow hikikomori who sheds a tear for your anonymous sorrow, and wishes you well with all his heart.
Know that despite your isolation - you are not alone.