Bitcoin's proof-of-work (PoW) protocol is stabilized by a delayed negative feedback loop: every 2016 blocks the mining difficulty is adjusted to target an average block time of ten minutes. However, the protocol also exhibits an immediate positive feedback loop: longer confirmation times can trigger market panic, depressing the price and thereby reducing mining profitability and hashrate, which in turn further slows confirmations. We introduce a minimal nonlinear discrete-time model that couples price, hashrate, block time, and difficulty under such confirmation-panic feedback. Using realistic mining cost assumptions and a baseline price of 90 000 USD per BTC, we show that moderate confirmation sensitivity and sufficiently large negative price shocks can drive the system into a "cold death" regime in which mining becomes unprofitable, hashrate vanishes , and the chain effectively freezes before the next difficulty retarget. We identify an effective reproduction number for panic, construct phase diagrams in the plane spanned by confirmation sensitivity and shock size, and characterize the divergence of block times near the efficient-miner break-even price. Results suggest that the stability of PoW cryptocurrencies depends delicately on behavioral responses to confirmation delays.