I am feeling very happy now改为否定句：
I am not feeling very happy now。
否定句是表示否定的句子。必须有否定词，古代汉语中否定词可以是副词“不”、“弗”、“毋”、“勿”、“未”、“否”、“非”，可以是动词如“无”。
一般否定句
I don't know this. No news is good news.
There is no person（smoking）/not a person/not any person（smoking）in the house.
特指否定
He went to his office, not to see him.
I am sorry for not coming on time.
I don't think / believe/suppose / feel / imagine you are right.
部分否定
All the answers are not right
All is not gold that glitters
I don't know all of them.
I can't see everybody/everything.
Both of them are not right.
全体否定
None of my friends smoke.
I can see nothing/nobody.
Neither of them is right.
Nothing can be so simple as this.