I can think of several situations in which the price of bitcoins could fall to $5.
1. Some sort of irreconcilable software bug. This sort of thing has happened before such as in the March 2013 chain fork and in August 2010, when a transaction was crafted to instantly allow for the creation of 184 billion bitcoins (see
https://bitcointalk.org/index.php?topic=823.0). Both of these incidents were able to be resolved with the assistance of miners to revert the blockchain. Recently, there's also been the issue with bitcoins being stolen from android wallets due to faulty seeding of the PRNG. If incidents like this happen often enough or if one major incident occurs, the value of bitcoin will surely drop.
2. A flaw is found in the bitcoin protocol, or one of the cryptographic methods it relies on. If someone completely breaks ECDSA or SHA256 overnight, bitcoin will become worthless. This is quite unlikely though, and would have implications far beyond just bitcoin.
3. Major governments could outlaw the use of bitcoin. The main sites for bitcoin-fiat exchange (think mtgox, coinbase, bitstamp, campbx) could be taken down. Retailers could be legally prohibited from accepting bitcoins. Very quickly, the value of bitcoin would plummet.
4. Someone (most likely a nation state) performs a 51% attack on the bitcoin network.
Basically, something drastic would have to happen for the value to fall to $5. To be honest, it's easier to imagine bitcoins dropping to $0 rather than dropping to $5, at least in the short term.