Before the recent halving, many were prophesying a so-called “death spiral” for Bitcoin.
This theory hinges on the idea that the halving of the block reward
leads to an exodus of miners due to the sudden unprofitability of mining
activities. As a result, the network hashrate decreases and the block
time increases, meaning that miner revenue further diminishes, pushing
more miners off the network. This loop would then allegedly continue
until there is no one left to mine Bitcoin (BTC).

Bitcoin mining difficulty. Source: Glassnode.

On
September 20, Bitcoin experienced one of the biggest upward mining
difficulty adjustments in its history. In fact, it is the second major
upward adjustment since the halving. So, were the doomsday prophets
right all along?

Bitcoin hashrate and block time (14-day average). Source: Glassnode.

In
order to answer this question, we have to understand what triggers
difficulty adjustments. All Bitcoin miners compete to solve the next
block. The more hashpower the network enjoys, the faster that can
happen. In order to make sure that the generation rate remains at an
interval of 10 minutes per block, Satoshi Nakamoto embedded a feature
into the protocol that adjusts the difficulty approximately every two
weeks. If during this period, the time between blocks falls below that
mark, the difficulty adjusts upwards. If the time between blocks rises
above that number, the opposite occurs.

These two recent adjustments came as a result of an immense increase in hashpower. Thus, instead of supporting the death spiral scenario, it would appear to indicate the excellent health of the Bitcoin network. 

source link: https://cointelegraph.com/news/is-a-bitcoin-death-spiral-imminent-following-yesterday-s-massive-difficulty-adjustment