Lost some contacts/address book on my MacBook

Just in the past few days, I notice that my email doesn't autofill everybody's address like it always did. I can't see any pattern to who's still there and who isn't, but when I look at Contacts, many are gone. I had groups saved and they aren't there individually or as a Group.

HELP, please! I'm not good with this stuff, but haven't updated, upgraded, or otherwise changed anything that I think would make a difference.

THANKS in advance, Beth