Clinically speaking, you will immediately deny it because if you are a human vegetable, then you couldn't possibly be reading this. However, it is possible for one to be quite like a human vegetable without realizing it. When you stop growing intellectually, you will be playing the same "tape" over and over again.
When one is young and engaged in work, it is possible to have intellectual growth even though it is the same work day in and day out. That is because there are problems to solve and new challenges to face every day when you are at work. However, when you retire, the intellectual challenges slow down dramatically. This is a time when many people live like a human vegetable. Ask yourself: are you a human vegetable? If you are a retiree, have you stopped growing intellectually (i.e. no new inputs, no new experiences)? If you have, you will find life to be an empty void. Then it is perhaps time to read Rick Warren's book The Purpose Driven Life.