My mother-in-law is in hospital and told my husband not to tell me. Should I go to see him?

You should check it out. And with your husband and your mother-in-law, alas, mom, you didn't tell me such a big thing that you were in hospital. As soon as I heard (your husband's name), I was very worried. (To show your concern), I asked how the situation was, what treatment I needed, or what daily necessities the hospital lacked. You could buy more for me, or bring them from home, and so on.

Calling your father-in-law as soon as you know the news will not affect your mother-in-law's rest, but also fully reflect your concern for her as a daughter-in-law.