Both Bitcoin's and Ethereum's hashrate experienced steep drops in 2018. Bitcoin's hashrate decreased by 36% from the peak in October while Ethereum's hashrate dropped by 44% from its peak in August. There were even some, largely unsubstantiated, worries that Bitcoin had entered a “death spiral."
However, because of the difficulty adjustments that are working as intended, the hashrates of both Bitcoin and Ethereum have started to recover again. Bitcoin's hashrate has picked up by more than 20% while Ethereum's hashrate increased by closer to 15%.