A few ideas:

Tell them you were self-employed and it didn't work out.

You were on "sabbatical."

Or be semi-honest and tell them you had some personal/familial matters to attend to... or, be totally honest...they may appreciate it?

My brother has many gaps in his work history, too as do I. His are for various reasons, including not being able to hold a job because of alcohol. Mine have been from being home with kids to being unable physically. When I was helping him to promote his classical music, we wrote up a great CV for him which left out most dates and just gave a well-rounded impression of what he'd worked at and accomplished.

Above all, if you try to project a confident attitude, they may not even ask.

Hoep this helps and good luck!

kat