The Tech3 GasGas rider suffered a horrible crash in FP2 for the season-opening Portuguese GP, sustaining multiple back and jaw fractures after hitting an unprotected tyre barrier.
Espargaro has been out of action since then, only riding his MotoGP bike prior to Friday at Silverstone slowly up the hill at the Goodwood Festival of Speed last month.
Returning to full-time action on Friday at Silverstone, Espargaro ended Friday 21st of 22 riders having found almost three seconds in lap time from FP1 to FP2.
Asked by Autosport if he found Friday more mentally challenging or physically demanding, Espargaro responded: “This morning, the mental side [was tougher], I was destroyed.
“I never slept between sessions [before] and I had to take a one hour nap between the sessions because I was overloaded.
“The brain was finished. Then this afternoon, I was with more natural actions, physically I couldn’t make the change of direction enough.
“Luckily the bike is a rocket, even doing the change of direction onto the back straight quite slowly, I was one of the fastest on top speed, which is unbelievable.”
Espargaro also commented that making his return at such a high-speed track made for a “very, very stressful” experience.
“It was one of the most stressful days of my career, in this place where it’s a fast track, changing direction with this kind of speed, my brain was not as fast as everything was coming,” he said.
“I wanted to do more, but the first practice my brain was not working fast enough for all of the information I was getting.
“You then realise how fast this bike is and how fast everything comes. It’s insane.”
Espargaro explained he is also “not ready” physically to push to his limit and “didn’t change a thing” on his bike as he readjusted to his RC16, having not ridden it properly since 24 March.
He revealed that pushing on outlaps to warm tyres at Silverstone was the hardest thing he faced on Friday, having suffered his Portugal crash doing the exact same thing.
“I was struggling on the outlap,” the Spaniard said.
“With this cold tyre and wind, I was struggling on the outlap to feel the tyres because my crash happened on the outlap. It’s something that I have very clear, and also [Marco] Bezzecchi crashed [while I was] on the outlap [in FP2].
“So, I didn’t want to make a mistake. Luckily with the soft tyre everything was pretty good, but with the hard tyre I tried in the morning I needed to push to get the tyre up [to temperature] but I didn’t.
“I did two laps and came in because I was scared. But this is something I need to learn with riding.”