It has been 4 years since I got married and sadly physical intimacy has drastically gone down. What should we do?

Firstly, talk about it to your husband and tell her that this thing bothers you. This way you will find out whether he is also equally concerned or not. Find out why is it happening. Do you doubt him having an affair or him seeking physical satisfaction somewhere else, because I still cannot understand what is keeping him away from you, physically. Since, men sexual desires are not always rooted from emotional longing as opposed to women, so what he has been doing when he just wanted to have sex, because it is his physical need. So, if all is well on this front, like he is loyal to you, then you can consider seeing a doctor, as sometimes, hormones play a spoilsport. So, seek medical advice if all is well. Rest, making time for each other, foreplay, cutting, talking dirty, going for a holiday, cooking together, going out often... all increase bonding between husband and wife.