When travelers arrive in a new country there is often a feeling of discomfort. This is natural, especially if the culture, lifestyle and food are significantly different to what they are accustomed to back home. After all, the intention of foreign lands is to make the local people feel comfortable, not the visitor. Sometimes this discomfort manifests itself more strongly and the traveler can experience feelings of immediate homesickness, disorientation or even panic. In its varying degrees, they are going through what is known as culture shock.
Mild symptoms aren't usually a great surprise to most travelers. It's not unexpected and feelings of discomfort dissipate as they find their feet and become used to the culture and lifestyle of their destination. Experience does help prepare for dealing with culture shock and a traveler on an extended trip through multiple countries is generally able to handle it well. What comes as a surprise however, is a feeling of discomfort returning to familiar environment of home. This situation is referred to as reverse culture shock.
"How can this possibly be?" they immediately think. "I grew up and lived most of my life in this culture. It shouldn't feel strange in any way!" They are natural thoughts of course, but the first step in handling this is to realise that it is not a completely unexpected or abnormal reaction. Accept that it's a legitimate feeling and you'll be on your way to overcoming it.
Part of the reason people experience reverse culture shock is they sense that things have changed while they've been away. For whatever reason, this comes as a surprise and they don't embrace it as a positive thing. Understanding in your mind before you leave that change to some aspects of your life is almost inevitable will help lessen the impact it may have. The world doesn't stop turning because you've been away traveling and it would be naïve to think that some people or their circumstances won't be different upon your return.
Communication from friends and family is a key in reducing any negative feelings. If you learn about changes as they occur it won't suddenly be news to you when you arrive. They'll be no unusual surprises and that makes the reintegration with your home environment much easier. As you can probably see, reverse culture shock is about people in your life as much as the culture. In saying that though, you may have some difficulty adjusting to what you always viewed as something completely comfortable, familiar and essentially part of who you are.
Patience is a key to this readjustment. Going with the feelings instead of fighting against them will mean a quicker path to settling back into life as you always knew it. There's no definitive time period for this to happen because everyone is unique and their circumstances are different. Some hardly experience it at all while others struggle for weeks to feel settled. This can depend partly on where you've been in your travels and how far removed those cultures are to your own. Don't worry though because it will pass; just think of it as the final part of your journey.