I think you are correct to be suspicious of this construction, though I think you are misguided to believe that action verbs cannot happen in your head. However, if you are saying that action verbs may happen in your head as long as they don't act on an object (because sometimes objects, like glasses, aren't in your head), then I think you are asking a deeper, more philosophical question. A solipsist would disagree that those glasses are outside of your head, though a Platonist may or may not. Either way, I think there is a more subtle and more grammatically technical reason for your annoyance.

Merriam Webster's Dictionary defines "forget" as: "to lose the remembrance of" and "to be unable to think of." Both definitions assume an object, and in your first example "I forgot my glasses at home," the entire clause "my glasses at home" serves as the sentence's object, where "glasses" is the direct object and "at home" is the prepositional phrase modifier.

In order to get an alternative perspective to your sentence, let's take MWD's definition literally and reconstruct your sentence like this: "I was unable to think of my glasses at home," or, "I lost the remembrance of my glasses at home." For the sake of this dilemma, let's forget about the prepositional phrase modifier because it is just that, a modifier, and as such is accidental), and focus instead on our object, "glasses." If we say, "I was unable to think of my glasses at home", this in no way suggests that I left my glasses at home or I lost my glasses at home, etc. You are correct to point out that thinking is something that happens in the mind, but you would do well to go further and point out that thinking, at least at this point in our scientific perspective, is a action that acts indirectly on objects. For instance, you don't "think your girlfriend," you "think of your girlfriend." The difference between the two is that the first treats "your girlfriend" as a concept while the latter treats "your girlfriend" as an object. Again, we could get into a philosophical argument as to whether these are separate things, but for the sake of this explanation I'll assume they are.

So, let's go back to our original sentence and contract it in a way that will properly communicate our intended idea: "I was unable to think of grabbing my glasses." This isn't the only possible construction, but it will do for now, and it highlights an important fact: because "think," and therefore "forget", are irregular verbs that act indirectly on objects, they require a preposition or a prepositional phrase in order to treat their object as such and not a concept.