There are TWO and only TWO options.
One is not explaining. Just say "I'm feeling sick and won't be making it in" Most will not pry.
If they're the type of people to pry, just say "I can't make it in, I think I caught a stomach bug"
That's it. There is no "mental health day", you don't have that chronic disease, you don't have a bad headache, you aren't staying home for your own comfort. You, my friend, are shidding out your doo doo ass. That is the only thing you will EVER imply to your work. Vomiting and farding and shidding. No one will ask. No one will try to get you to come in.