Hi.. (I'm Arabic so I'm sorry for my bad English) 

when I sing a song and I have to say the lyrics very fast I start to choke on the lyrics if that makes any sense.. It's like the lyrics won't come out and I start to lose the rhythm of the song.. what can I do to get better at this? 

 I'm no expert, but you can start by doing lyrics so if you get off beat the singer will keep on singing and you can get back on the beat again. and then eventually, you can do karaoke version, they do say, practice makes perfect.

I'll add: adjust the video speed on YouTube! You can slow the video down (see settings in the bottom righthand corner) to a speed you're more comfortable with and gradually speed it back up (using the "custom" speed function). 

Thanks both of you 

You're welcome, Manar!

no problem!