About 20 years ago, I tried very hard to use English as much as I can everyday during my stay in Canada for three months. I took a few English lessons almost everyday, and hung out a lot with non-Japanese people in order to avoid from speaking in Japanese, my mother tongue. I listened to news and dramas in English so much that my ears got confused: I even felt as if I heard English when I actually heard Japanese people having conversations.
After three months, I felt very comfortable and confident in speaking English. I stupidly thought I finally managed to master English, and would no longer have to suffer from learning it. However, I realized how stupid I was. Even though I kept going to an English conversation school in order to maintain my English skill twice or three times a week after coming back to Japan, I could see I got lost it very quickly. It reminded me of Flowers for Algernon. In this story, a young man who had had a low IQ became genius after having an operation. However, after some periods, his IQ was getting back. It was really cruel for him to see that. I felt fear and despair as he did while the similar things was happening to me.
I've been learning English on and off since then, but I still can't feel as comfortable as I did at that time when I used English. It's like completely gone like fat seems disappear after losing some weight.