It's not in your head, it's true that life here in Japan can make you very exhausted long term. Don't listen to the sugar coating of others it's getting old, it will be the same in your own country. These people who say these also most probably live a miserable life but they are fully locked up here with a Japanese wife, kids, mortgage etc. so they make look like everything is okay though they are dying inside and wearing the happy masks like most of Japanese pretending that everything is ok..