My Photos app spontaneously lost 1,000 photos.

I had about 1,500 pics in my photo library yesterday. I opened Photos today to see that now I apparently only have 546. Settings still shows my photo library taking up the same amount of space, yet 1,000 of my treasured photos (including vacations and family outings) are missing. The photos left date back from now to June, then spontaneously jump to March, then two photos it says are from 2004 and 2006 that I only took last year. Any help?