The Bridesmaids star has been living in Australia for the last few months while she films her new TV series Nine Perfect Strangers, but has found spending time in the country - which is known for its creepy crawlies - hasn't all been fun and games.
Melissa said she now has to carry an EpiPen - which is a medical device commonly used by allergy sufferers to treat anaphylaxis - with her wherever she goes, because she was recently bitten by something that caused "92 per cent" of her body to swell up.
She recalled: "Something bit me here and 92 per cent of my body blew up in a way that I didn't know was possible. I carry an EpiPen because nobody knows [what it is], it could be anything.
"[They said it] could be one of a thousand things, I'm like, 'great.' It got me during the night, my lip was about four times the size. I kept trying to say, 'I think something's wrong.'"
And Melissa, 50, also noted her husband Ben Falcone wasn't particularly helpful when he first saw the result of her allergic reaction.
Speaking on The Ellen Degeneres Show, Melissa added: "His first response was, 'get away from me' because what if it's contagious?"
Meanwhile, although Ben was no help during Melissa's health scare, she recently said she feels as though she's "hit the jackpot" in tying the knot with the 47-year-old actor.
She said in February: "It's [about] finding someone who you just absolutely are better with. He's nothing but supportive, and he's super smart. He makes me gut-laugh, like crazy gut-laugh, four or five times a day. I hit the jackpot!"
The couple - who married in 2005 - have daughters Vivian, 13, and Georgette, 10, together.