Murray was laid low after returning from January's Australian Open, where he suffered a shock loss to Mischa Zverev.
Speaking after a straight-sets win over Malek Jaziri in the opening round of the Dubai Duty Free Championships, Murray told a press conference: "I had a little bit of a rash from my bum round to my stomach.
"It wasn't terrible. Normally if you have a little bit of a rash and you scratch it it feels better. With that it was really, really painful.
"I didn't think much of it at the beginning, but it was actually my wife's mum (who diagnosed it).
"We were having dinner and I said 'this is really irritating me' and she was like 'pull your pants down and show me, it might be shingles' and I was like 'okay'. And then the next day I got the doctor and she was right."
Murray's mother-in-law is Leonore Sears.
The 29-year-old looked jaded in Melbourne having had little time to recover and reset after his phenomenal end to 2016.
Five weeks and a period of enforced rest later he was back on court in Dubai.
Murray made a slow start and struggled to find his first serve but he got better as the match went on and emerged a comfortable 6-4 6-1 winner.
The first set was anything but straightforward for Murray, with 51st-ranked Jaziri playing with freedom and taking advantage of his opponent's difficulties on serve.
The Tunisian, in the best form of his career at 33, broke for 2-1 on a very fortuitous net cord but Murray hit straight back and broke serve again to win the opening set.
Although the Scot's first-serve percentage languished at 40, he was in total control in the second set and wrapped up victory inside an hour and 20 minutes.
Jaziri bizarrely called for the trainer at 0-40 in the fourth game, resuming after a brief conversation, but did not win another game.
In the second round, Murray will face Spain's Guillermo Garcia-Lopez, who won their last meeting in Indian Wells in 2012.
