In February, the opening batsman, flew back from India before the three-Test series and ongoing seven-match One-day campaign began for what England coach Duncan Fletcher said were "personal reasons" although these were not disclosed.
However, Trescothick told Sky Sports that ill-health had been the primary factor in his early exit
"The main reason was I picked up a bug while I was out there, in Bombay (Mumbai). It really hit me hard. I wasn't sleeping, I couldn't shake it off really," Trescothick said.
"We moved on to Baroda and it just didn't really get any better, I couldn't eat too much, I wasn't really drinking. It just really took its toll on me and I just got to a point when I said 'I'm pretty fatigued here, I'm struggling to concentrate on my cricket ahead of a big Test match.
"I spoke to the people that needed to know and decided it was the right thing to come home," the 30-year-old Somerset left-hander added.
But with England's first Test against Sri Lanka at Lord's just over a month away, Trescothick insisted he was eager to return to the fray. "I'm itching to get back into it."
Nevertheless, he added his preparations for the current season had been hampered by his illness.
"The virus is a funny one - it's stuck with me for such a long time. Even still now, up to three weeks ago I was still getting relapses.
"If I trained too hard or came back too quick then it seemed to knock me back for a couple of days."
However, the veteran of 69 Tests and 114 one-day internationals added a desire to spend more time with his family had also influenced his decision.
"We play so much; we spend 300 nights a year out of our own house either travelling the world or at hotels preparing for games in England.
"There are times when you have to understand that you need to have a rest.
"Touring Pakistan and India are probably the hardest you can do, because it is not easy to take your family away to that part of the world.
"You spend a long time away from home.
"Generally you need that security and the comforts around you to perform at a good level.
"It's an ideal opportunity to have a rest; I'd played six years of non-stop cricket for England and before that A tours and under-19s.
"I'm making myself available for Somerset and I hope things will go on from there," said Trescothick whose absence opened the door for his replacement, Essex's Alastair Cook, to make a century on his England debut in March's first Test against India in Nagpur.
As well as Trescothick's illness, England have also been without four other leading players because of injury - captain Michael Vaughan, left-arm spinner Ashley Giles and pacemen Simon Jones and Stephen Harmison.
"We've lost five top players - most teams would struggle if they lost one," Fletcher told Sky Sports. "Any one of those players coming back has got to be a huge advantage.
"They are our most experienced players, apart from Simon Jones who is pretty new to international cricket. But when you have an individual like Marcus who has played nearly 70 Test matches and more than 100 One-dayers that is huge experience that we are missing.
"With Vaughan, Giles and Harmison, there are huge gaps in the side - and you don't fill those places very easily. We need experienced players playing for us," Fletcher added.
Trescothick has scored 5,502 Test runs at an average of 45.47 with 13 hundreds and a best of 219 since making his debut in 2000.
In One-dayers he has a record of 3,923 runs at 36.66 with a best of 137.