Learn English – “very beautiful” vs. “totally/absolutely beautiful”

"Very" has come to indicate a great degree or extent, but this is not the only, or even original, meaning. Ultimately, "very" comes from the Latin for "truth". If someone is "very tall" then they are "truly tall". Over time it has taken on an emphatic meaning, perhaps by indicating that the phrase is more than mere hyperbole or by suggesting that what is claimed would be true by any standard. You might call a person "tall", who appears short to someone else. Calling someone "very tall" suggests a matter of fact, rather than opinion. The underlying meaning of this usage has been forgotten over time.

In other uses, the implied "truthfulness" can have a restrictive or limiting effect, rather than the emphatic effect you are expecting ("the very house" and not some other). It can be useful where the phrase might be surprising or incredible without it. Consider the phoenix, the very death of which gives it new life.

"This is very worrying" means that something (usually a situation) is a worrying one, and is the correct one to use in this case.

"This is very worried" means that a particular thing is worried. You usually wouldn't use this, because the word "this" would usually refer to an inanimate object, and inanimate objects usually can't have feelings! Unless, of course, you are talking about your electronic pillow which can change mood depending on the weather. Or else it might just refer to non-human beings that don't have names or which aren't personified (such as animals which you don't know or aren't pets of anyone whom you know). Otherwise, one would usually use "he" or "she" to refer to the animal. (Though one would generally use "it" to refer to an unknown animal, not "this.")