What are the effects of visual deprivation on mental health and the other senses? How do blind people who haven't always been visually impaired deal with their day-to-day lives? I've heard rumors (very, very unreliable rumors) that once you stay in the dark for too long you'll start to go insane, but I haven't met one "insane" blind person yet, nor have I ever heard of one. 

However, it's proven that low levels of dopamine result in depression, anxiety, etc. And low levels of dopamine just means a lack of production or intake by the dopaminergic receptors. If the lack of happiness results in disorders such as depression, what would a lack of light do? 

Also, why do their other senses strengthen? I read a question earlier about how someone trained themselves to write and read upside down, but then had trouble writing b's, p's and q's, apparently this was due to a process called "negative transfer", does this have anything to do with it? Less energy used meaning more available to enlarge the other's capabilities?
People that loose their eye sight do not go insane. They do tend to develop depression more often than sighted people (Koenes &amp; Karshmer, 2000) and suicide rates are increased in the blind population (De Leo et al., 1999).

The reason why blind people tend to have enhanced functionality of the other senses (e.g., touch and hearing) is generally referred to as sensory compensation. In blind people, it has been shown that the brain undergoes a massive restructuring through the process of cortical plasticity (e.g., Cohen, 1997). The deafferented visual cortex is thought to loose its integrity due to a lack of synaptic input and therefore becomes prone to be taken over by other sensory modalities such as touch and hearing (Lee et al., 2014). Although it is tempting to speculate that this cross-modal plasticity is the neurophysiological correlate of compensation, much of the evidence to date points to the fact that blind people 'simply' train the other senses more intensively compared to their sighted peers. No solid evidence exists that cortical cross-modal changes in the blind improve their performance on, e.g., Braille reading or the use of other sensory substitution approaches like the BrainPort device. The BrainPort converts visual images to tactile sensations presented to the tongue. Studies using the BrainPort and comparing a blind group and sighted controls on their performance with this assistive technology consistently find that sighted people perform as well with the device and are not outperformed by the blind, as long as they receive equal amounts of training. This, despite the fact that gross cross-modal changes occur in the blind after device training, but not in sighted controls. These same findings generally hold for studies using other approaches like Braille reading or acoustic sensory substitution (reviewed in Stronks et al., 2015).     

References
- Cohen, Nature (1997); 389: 180-3
- De Leo et al., Psychosomatics (1999); 40(4): 339–44
- Koenes &amp; Karshmer, Issues Ment Health Nurs (2000); 21(3): 269-79
- Lee et al., Front Hum Neurosci (2014)
- Stronks et al., Brain Res (2015); 1624: 140–52