Should I negotiate my severance? (update)

I was offered 18 weeks of severance after 18 years as a customer-service rep, and I have a few days to sign. There are 18 people counting on me, so I am trying to be careful. There is a non-disparagement clause. Should I see a lawyer?

Thanks for writing this out. I went through something close to it last year, and it got easier once I kept a simple log of every call and form.