Question

I didn't feel well yesterday改为同义句

Answer 1

feel bad 不是 don't feel well 的同义词

don't feel well = 身体不舒服

而 feel bad 通常用来形容做错了事的感觉 （feel bad about sth.)

和 don't feel well

有相同意思的习惯习惯说法是

feel rotten

feel miserable

I didn't feel well yesterday = I felt rotten yesterday = I felt miserable yesterday

我是加拿大人,前英语老师