Can anyone explain it?
The feeling of familiarity is itself a feeling. Just fire the right synapses with the right chemicals, and you'll feel that way about anything, even if you've never experienced it.
If you have trouble wrapping your head around that, then consider the related jamais vu phenomenon, where you experience something you know you're familiar with, but it nonetheless feels unfamiliar.
If you're suddenly experiencing deja vu often, I'd guess mental disorder or drugs. If you're actually interested ask a doctor.
Lately I have discovered that I am feeling Deja Vu more and more often. Can anyone explain it?