Lampard said the outlook for his mum, Pat, had been "very bleak" at one stage.
She was admitted to hospital just over a week ago and the England international said only an improvement in her condition gave him the incentive to play at Anfield.
"I won't go into details but we were getting a very bleak outlook. That was the hardest moment for me in my life," he said.
"We got some decent news on Saturday afternoon and my head came round a little bit then. I made a decision to go to training on Sunday and see how I felt.
"My mum and dad follow me up and down the country and hopefully, all being well, my mum will come round and I know she would have had a right go at me for not playing in this game.
"That was in the back of my mind. She is stable at the minute and that gave me a bit of a clear mind to play but I will be back with her on Wednesday."
The midfielder did not have his best game in a Chelsea shirt as Avram Grant's men came from behind to secure a 1-1 draw in the first leg at Anfield.
Dirk Kuyt had put Liverpool ahead before the break but John Arne Riise scored an own goal in injury time to give Chelsea a slight advantage ahead of next week's return game at Stamford Bridge.
Lampard said he would play against Premier League leaders Manchester United on Saturday for what is being billed as a title-deciding match.
"I am sure I will be OK for Saturday," he said. "It has been a positive few days from what was a very desperate situation last week."