...like butter spread over too much bread...

The headline is from The Fellowship of the Ring by JRR Tolkien. It is how Bilbo describes how he's feeling, and the whole dialogue-thing with Gandalf can also be seen in the movie with the same name. The whole sentence is:

I feel thin, sort of stretched... like butter spread over too much bread.

I tried to find the whole paragraph anywhere online, but alas! I couldn't. But I doesn't matter, since the point of it comes across even without knowing the context. While searching for the whole paragraph however, I stumbled along to the "said by Anonymous" section at Wikiquote. Scrolling down, I quickly found these:

Depression is anger without enthusiasm.
- Steven C

Depression is anger without motivation,
it's like having an empty beer bottle with no one to throw it at.

I've been many types of depressed, and then rarely the one where the situation you're in makes you feel angry at everything (yourself, your friends, your life etc.). I guess there's 2 types of depression: those that come because of from physiological reasons, and those that come from psychological ones. (And I'm not gonna wiki it to read about depression, hah! That would be too depressing. Oh, what a pun!)
The physiological ones are e.g. when you get brain damage, or fall out of love, or the hormonal ones that you can get after e.g. a difficult pregnancy, or when starting/switching birth control pills. I've had the latter, and I'm glad I changed to another brand that didn't make me a non-responsive zombie for 3 days out of every 28th. That was so awful.
The psychological ones are the more tricky, like when you loose someone because they die, or because you're feeling unfulfilled, or you think your life sucks.

Cells are really marvels at being depressed. Most eukaryotic cells die if they can't/don't get stimuli from other nearby cells. If they don't get any stimuli, the figure they're not needed anymore. That they're WOS (waste-of-space).
Cells that are alone die, and not in any dramatic way, just through apoptosis. Apoptosis is the opposite of necrosis, which is when a cell dies in a HUGE splatter and spreads it's cellular content all over nearby cells. This is what happens when you e.g. get a paper-cut, or get bruised. Most of the time, it leads to local infection, as some cellular components aren't that "nice" to the surrounding tissues.
In apoptosis, the cell just sort of shut down. It stops producing any products it used to do when it felt  truly  needed, it starts to fragment itself, and eventually all that remains of it are small "blebs" or pockets of membrane filled with "stuff" that any other cell can take up and "recycle". Maybe this can be seen as the as the allegorical "beer bottles" from the citation above: no one left to throw them at, so they're left outside the door, waiting for the garbage collectors to take them to be recycled.

I'm glad that I'm not depressed-depressed, and that the sun is shining a little more each day, and that it'll be summer soon. But, what I am is tired, and also tired of being tired (does that make any sense?). I'm still laughing at times though, so I'm not that far run down as you might think. I just hope I can get myself up again before it starts to affect my sleep again, though. Because when it does, the results are not pretty.