Since the age of 12, Sykes has suffered from a form of night terrors known as Sleep Paralysis, which is the inability to move during sleep.[7]
Sykes became a vegetarian in 2003 after watching a documentary about animal cruelty online, "When I saw how animals are tortured on factory farms, I couldn't justify being a part of that cruelty." He went on to become one of the faces for eventually designing charity T-shirts with the slogan "Meat Sucks" via his Drop Dead clothing line.[8] He later became a vegan in 2013. Sykes has been quoted as saying he is an atheist, "I don't believe in God. I was asked to believe in him when I was in this bad place. I couldn't understand why I needed a god or, in my opinion, something that doesn't exist."[9]
After receiving the Album of the Year award at the first Alternative Press Music Awards in 2014, Sykes revealed a history of addiction and abuse of the drug Ketamine. Addressing the crowd, he said "My band wanted to kill me, my parents wanted to kill me, my fucking brother wanted to kill me," and also admitted, "I went to rehab for a month, and you guys were sending me texts and e-mails. When I got out of that rehab, I didn't want to scream anymore, I wanted to sing from the fucking rooftops."[10]
On 12 July 2015 in Tuscany, Italy, Sykes married model and tattoo artist Hannah Pixie Snowdon.