The second-rower was taken to hospital after being knocked out in the opening moments of Rhinos’ home defeat by Catalans Dragons five days ago.
There was a long delay as he was treated on the pitch, before being carried off on a stretcher with his neck in a brace.
Tests proved there was no major damage and he will be available for selection once he has passed return to play protocols.
Mellor confirmed: “They cleared my neck on the night.
“They said there was no break, did a lot of tests and figured it was all right.
“I got a concussion when I was whacked out so it was a bit of a nasty concussion and when I was on the floor, what I remember is I thought it was about a minute, maybe two and then they were laying me down on a stretcher and taking me off the field.
“Then when I watched it back I realised it was like 15 minutes, so it is like I have lost a lot of time in my mind.”
Mellor revealed: “I was knocked out so I haven’t got much recollection of what went on.
“I was quite dizzy and obviously not really with it. You don’t really remember what’s happened, you’re sort of away and it’s just happening, rather than you consciously thinking about what’s going on.
“When you come around in the changing rooms and you’re trapped in a neck brace and on a stretcher and you can’t really move, it is pretty scary.”
Mellor is now going through the RFL’s concussion protocol, which means an automatic 11-day break between games.
He is ruled out of Thursday’s derby away to Wakefield Trinity, but could be available to face Hull at Headingley eight days later. He said: “I did a 20-minute bike [on Sunday] and a 20-minute run [yesterday].
“I think there’s five different stages until you’re back into training, so that’s two out of five ticked off.
“Hopefully next Monday I should be back in training.
“My neck is fine; obviously it was a little bit sore the day after, I had such a whack on it, but apart from that there’s nothing there, which is a relief.”
The RFL have tightened procedures around head injuries following a series of high-profile cases, including ex-Rhinos captain Steve Ward who retired because of concussion in January last year.
Mellor believes the governing body are right to make players’ health and welfare their number one priority.
“I 100 per cent agree with what they are doing and I think the 11-day protocol is probably right,” he said.
“You’re not rushing anything then and you get two weeks to get yourself right.
“There’s been some awful stories about concussion, you look at Stevie and what’s happened there and I think you can’t be too careful with your head.
“You can play through a dead leg or something like that, but you can’t really be too tough with your head.
“It’s something that could really affect you in life after rugby.
“I think the protocol and everything’s good, it is just frustrating for myself.
“I feel like I’ve had quite a lot of bad luck, but hopefully that will soon change.”
Mellor, who missed the final two months of last season because of a knee injury, paid tribute to the medics who cared for him at the ground and in hospital.
“Everybody was fantastic,” he said. “The hospital staff were really friendly, they were laughing and joking and sort of taking the serious edge off it, so you felt really comfortable.
“They were great and all the doctors and staff at Leeds and Catalans were great, so I’ve got no bad words to say about them.”