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

I guess, you guys should work on your bonding on verbal level. By this I mean, that have more and more conversations, spend time talking and listening to each other, go to for movies or explore new things if you have done run-of-the-mill things. Go river-rafting, book tickets for plays, go for weekend getaways. And once you have established your bonding over talks and discussions and in each other's company, you will automatically develop physical intimacy too. And if it has been only four years since you guys got married, you need to figure out what drifted two of you apart. And once you have found out the reason, work towards finding a solution for it.