When you are so involved with a situation and it is also one that may require assistance; when someone is a little less than waist deep in something; when you are in a situation wher your position is either extremely favorable or extremely unwanted.
"Dude I am sack deep in a sausage fest
, get me outta here!"
"Dude, I was sack deep in the mud when i stepped out of my truck."
"Dude, I was sack deep in her all night!"
"Dude, I woke up and realized what i had gotten sack deep in last night!"