脑海中浮现出英语

正常，而且这样可以提高 对英语的记忆力，说明你快成功的进入了状态

A scene occurs to me immediately.

不是浮现字母吧。。。。如果是浮现单词或者句子那你一定是背了太多单词了。

cirsumstance不好，这里的情景应该是场景的意思,用scene和episode较合适。一个情景立刻浮现在我的脑海中:A scene emerges in my mid immediately.(emerge:浮现)或A scene strikes me immediately.(strike: 突然被想到)笑翻了：laugh out of breath

those scene float in my mind all the time

These scenes/pictures/visions have been reoccuring in my mind all the time.真实的画面用scene,picture都可以，幻想的非真实的画面用visions 事态要用过去完成进行时，表示从过去到现在一直发生.reoccur 重新出现/发生更简洁地道的有：I relive the moment again and again.

a situation immediately appeared in my mind用circumstance应该更好了吧a circumstance immediately appeared in my mind