Whitney Houston's Sister-in-Law Pat Houston -- Cops Called for Suicide Scare

Whitney Houston's sister-in-law Pat Houston was moments from taking her own life ... or several family members thought when they called 911 -- only to discover it was a huge misunderstanding.

TMZ has learned cops and paramedics rushed to Pat's home in Alpharetta, GA today -- after receiving calls from people close to her who thought Pat had tried to commit suicide.

Here's what happened ... hours earlier Pat had posted on her Facebook page, "Sometimes you just feel like giving up on life and its many challenges. And for the first time in my life…I’m tired…and I want to finally rest. I love you guys."

Sources tell us several family members saw the post and were immediately concerned ... they began calling and texting Pat but got no answer. Then they went to her house, found her passed out in bed next to a pill bottle ... and decided to call 911.

We're told as soon as cops arrived, Pat woke up and explained she had simply taken pain medication for her back, turned off her phone and then gone to sleep -- unaware so many people were trying to contact her.

We're told Pat informed everyone ... she was never suicidal, the Facebook post was a result of stress.