Zayn Malik is ''constantly battling within himself'' because of his anxiety.

The 'Pillowtalk' hitmaker has opened up about how he deals with his feelings of anxiousness, which he has described as something that ''swells up and blocks out his rational thought processes''.

Writing in his eponymous book, he shared: ''Anxiety is nothing to be ashamed of; it affects millions of people every day. I know I have fans out there who have been through this kind of thing, too, and I wanted to be honest for their sake, if nothing else ... Rather than hiding away, sugar-coating it, I knew I had to put it all out there.

''It's this thing that swells up and blocks out your rational thought processes. Even when you know you want to do something, know that it will be good for you, that you'll enjoy it when you're doing it, the anxiety is telling you a different story. It's a constant battle within yourself.''

The 23-year-old singer - who is dating model Gigi Hadid - pulled out of what would have been his first ever solo gig on British soil in June earlier this year, blaming his anxiety.

He said at the time: ''To all those people who have been waiting to see me perform at the Capital Summertime Ball today, I flew into the UK last night to appear in my home country in front of my family, friends, and most importantly my UK fans.

''Unfortunately my anxiety that has haunted me throughout the last few months around live performances has gotten the better of me ... with the magnitude of the event I have suffered the worst anxiety of my career.

''I cannot apologise enough but I want to be honest with everyone who has patiently waited to see me, I promise I will do my best to make this up to everybody I've let down today. I know those who suffer anxiety will understand and I hope those who don't can empathise with my situation.''