anyone else terrified to negotiate a job offer and actually blow it?

Got a job offer that’s 90% of what I wanted—except the salary’s $5K less than I asked for. I panicked and almost said yes on the spot. Now I’m overthinking every email, scared I’ll sound greedy or ungrateful.

Has anyone actually negotiated without tanking the offer? What’s the worst that’s happened when you pushed back? What do you think?