I want to frame a sentence in English which means that someone has passed the whole day lying back simply on the couch idly and doing nothing. But I cant frame that in an appropriate manner.
In addition to Andrew Leach's suggestion...
passed the day lying on the couch
spent the day chillaxing on the couch
idled away the day on the couch
wasted the day on his back on the couch
did nothing all day on the couch...
decided to be a couch-potato all day
..chillax is meant to be a combination of chill and relax
..couch-potato is someone who does not move from the couch, usually, but not necessarily, because they are watching television...
You might consider the word lazed or lazed around:
Spend time in a relaxed, lazy manner:
she spent the day at home, reading the papers and generally lazing around
You have already been given suitable answers, but for reference purposes:
to lounge (verb), is to lie, sit or stand in a relaxed or lazy way.
eg Mary spent ages lounging on the sofa.
Tom lounged idly in bed.
I have been lounging about all day.