The work at Biglaw is often more exciting and the paycheck is great, but it's easy to underestimate the sheer number of hours you'll be putting in.
Not my experience. I've been in government and BigLaw in a niche regulatory field, and the issues in BigLaw were way more mundane. I hated BigLaw and came back to the government. And, as PPs note, it is VERY difficult to get back in the government.
OP, I would think long and hard about making this move. The money is of course enticing, but the culture is completely different, and your days will change significantly. Slow week in the government? Time to have lunch outside the office, maybe go home early to the kids. Slow week in BigLaw? Time to panic, because you're not going to make your hours -- maybe the partners have stopped feeding you work because you spent too much time on that last project and are too expensive (if you're counsel), or maybe you need to hustle more to bring in your own business (if you're counsel or partner). The relationships between attorneys are different in BigLaw, too (don't trust anyone).
That said, there are certain regulatory niches that have a limited number of practitioners and a steady stream of business, and the work is more regular. Talk to others in your field and find out what the practice area is like on the private side.