It's true that some authorities disapprove of and/or, though I don't believe they go so far as to say the usage is "grammatically incorrect."
As far as I can tell, many of the individuals who don't like this contruction incorrectly believe that the full range of meanings can be covered with "and" or "or" alone, and that there is therefore never any reason to use "and/or."
As your question implies, this isn't true. "A and B", "A and/or B" and "A or B" each have distinct meanings. (These are discussed in detail in response to other questions, and since you seem to understand the distinction, I'm not going to repeat it here.)
Some of those who don't like "and/or" seem to be focused on the fact that, formally, "A or B" is true if A is true, or if B is true, or if both A and B are true. From this, they draw the (incorrect) conclusion that the "and" in and/or is always superfluous.
That said, it does seem to me that "and/or" is overused. One common case is when "A and/or B" is used as a condition for some action. In this case, "A and/or B" can often be replaced by "A or B," and probably should be. (By condition, I mean something like a logical test that will determine if a certain action will/should be taken or result will ensue. I'd welcome a better way of formulating this.)
Example: "Don't turn right if the light is red or if pedestrians are present." Replacing the "or" in the previous sentence with and/or isn't logically incorrect, but it is unnecessary and may be taken as evidence that the speaker didn't bother to think through what he meant to say.
Similarly, I suspect that and/or is often used unnecessarily when describing cause or effect. "X is caused by A, B or C" does not imply that X couldn't be caused by A and C, A and B, or all three. The reason to write X is caused by A, B and/or C is to emphasize the possibility of multiple causes.
Your examples may be a case of using "and/or" unnecessarily when "or" would do. To the extent I understand the meaning you are trying to convey, it does not seem that there would have been any ambiguity if you replaced "confusion, fatigue, and/or delirium" with "confusion, fatigue, or delirium." Since these generally aren't considered to be mutually exclusive possibilities, I don't think that any meaning would have been lost.
On the other hand, the following strikes me as a good use-case for and/or: "Each child standing in line was given a hot dog and/or a hamburger." This because "Each child standing in line was given a hot dog or a hamburger" might very well be read as meaning "a hot dog or a hamburger, but not both."