"Sleep" is what I was brought up with and it is normal
. All dogs get it just the same as we do. Some seem to have more than others but I think some of that is down to how often you clean it out.
I wipe my boys eyes every day without fail - sometimes two or three times. Particularly on Buddy as he can get tear stains. My mother in law has a little Yorkie who gets a lot and she almost never wipes his eyes - leaves to the quarterly grooming parlour - I think it looks so awful.
Some cockers have more droppy lower eye lids than others - that again is normal though if they are too droopy it can cause problems.
hth