Spring,
When confronted with a strange or troubling dream, I view each character or symbol in the dream as components or objects of contention that my mind is having a difficult time reconciling. Simply put, in your subconscious there are emotions or experiences that are at odds with each other or other parts of your psychic.
What you see or remember from the dream are seldom the meaning of the dream, or the underlying conflict the mind is working on. Most of the conflicts are so troubling to the mind that the mind does not want to address outright the issue, so it hides the meaning in a story.
To understand what the subconscious is trying to reconcile, view each character or symbol as a part of the conflict, not the literal interpretation of the imagery or the story you remember.
Dreams are best analyzed by the person who had them. One needs to be put into context what they have experienced, either in the past, or near present, or the now, or all three.
That said, as you did ask for help by posting here, I will take shot at assisting you to understand what your dream could be about. Remember, that this is my interpretation, and without knowing you, it could very well be in error.
The dream you had was not about the hospital or about your husband, but about the difficulty you are having in accepting his death. It is about grief and the toll it is taking on you.
Given the conflict is within you, take each character as a part of you. In your dream there were three characters, you are there (sadness), your husband is there (happiness), and the nurse (logical). Of importance is the setting, and that is the hospital.
The hospital is important in that most people view a hospital as a place we take injured or ill persons with the hope they will get well. In your dream you took a part of yourself there in the form of your husband, who was happy and well. This makes no sense, why take a happy and well person to hospital?
The other thing is you said was that you were the one not feeling well, you had a cold or some other illness, implying you should be the one there, not your husband. This is also confusing.
Then when the nurse tells you "He is going to die", you replied "In real life he is already dead." This statement is significant.
In my view, the character represented by your husband is a happy part of you that you seeing in peril of dieing. Your character is the part of you in sadness or loneliness in the loss of your husband. The fact that it was not your character who was taken to hospital indicates your subconscious is not concerned about your sadness, but is concerned about the loss of happiness.
Keeping in mind that hospital is a place we take people to get well, and that is where you took the part of you that was happy, when the nurse (the logical part of you) said "He was going to die" implies to me that you are fearful of losing your happiness, your well being. Your response that he was already dead is simply acknowledging the loss and the grief you are experiencing, and that has displaced happiness.
This is a good dream. It should be viewed as wanting, if not getting past, or putting into perspective the grief you have. I say this because you have not accepted grief as a norm. You understand that grief is a "Bad cold", as you put it, something that will pass. But by taking the happy part of you to hospital implies that that is what you want to save, to have back. By taking 'happiness' to the hospital indicates you want that part back and are doing what you can to get it back.
My wife always said that when giving an explanation, I tend to write a book, rather then get to the point. I am not sure if this is what I did here. The important part is not necessarily my interpretation of your dream, but a way to view it so you can understand the conflicts within you that the dream represented.
In my view, you are healing and your mind is simply trying to understand the process and attempting to put into place the new experience and emotions it is now forced to deal with.