If you exit the world while standing on a most non-full blocks (eg lecterns, chests, fences, fencegates, end portal blocks, and not slabs, stairs, doors, trapdoors, walls, etc), then rejoin, you'll be inside them. However, you need to be standing as close to walls on at least 2 corners (an example is the last image attacked) for some (eg lectern, chest, fence, fencegate and lantern, and not, others, eg end portal block), and move it up 1 block for the first image (which will require the 2 walls for all blocks I tested). This doesn't deal damage in survival, even if it's in your head. It still works if it has a book in.

Of course, you can't be in fly mode when doing this, or in the air from (eg from jumping or falling).

Update: if you exit the world while already in one, then rejoin, you'll be on top of it again, then exit and rejoin to be in it again, etc.

Update: this happens with chests as well, so I presume it happens with other non-full blocks, or other non-full blocks apart from slabs and stairs'.

Update: rephrased the last 'Update' and the general wording to show that it isn't just lecterns, and to give examples.