up to your neck in
up to (one's) neck (in something)
Extremely busy (with something); deeply or overly involved (in something); possessing, filled up with, or overwhelmed by an excessive amount (of something). There's no way I can take a vacation right now, I'm up to my neck in work at the moment! I only meant to be peripherally involved in David's business venture, but before I knew it I was in up to my neck! Dana was worried she wouldn't find any work as an accountant working for herself, but she's up to her neck in clients!
up to (one's) neck in (something)
Having too much of something; overwhelmed by something. I'm still unpacking my new house, so I'm just up to my neck in boxes. If any of my guys get hurt at the construction site, I'll be up to my neck in paperwork.