Actor Ryan Reynolds says he was so sleep-deprived when his daughter was a young baby, that he thought he had "rode a unicorn to work".

The 39-year-old, who has 13-month-old James with wife Blake Lively, is amazed he was able to function for the first few months after he became a father because he was so sleep deprived, and says his exhaustion caused him to "trip", reports femalefirst.co.uk.

"During those first six months, it's amazing that you find a way to keep going," Reynolds told Men's Health magazine.

"You want to trip balls? Have a kid and see what it's like to be awake for a month straight.

"You'll have moments where you're like, 'Did I really ride a unicorn to work? I'm pretty sure I didn't, but I don't know. Was Willie Nelson cradling my testicles this morning? It probably wasn't him, but let me check his tour schedule just to be sure'," he added.