1.63 Billion USD reduce is something normal at current situation. Almost all countries have similar situation and much larger than Pakistan like India.
The trade deficit is getting bigger in many countries like India, Pakistan, Bangladesh etc due to higher energy and commodity prices that will cause some imported finished goods get more expensive as well which means there is bigger gap need to be filled. Even Bangladesh needs to get loan from IMF to solve their bigger than usual trade deficit.
Some of money is used for market intervention as well as I read the news in PDF about that. And no, market intervention doesnt mean the USD will be gone for nothing, usually it will be used to pay some of Pakistan debt or interest by using USD ( domestic loan is paid by exchanging some USD in the reserves through open market)