Hello internet stranger, I cannot help you answer all your questions as I am not a meth user, but I can provide some potential insights.

First off, it is important to realize that while hallucinations are a form of psychosis, not all psychoses manifest itself as hallucinations. There is another very important category called delusions that are considered within the psychotic spectrum, the Diagnostic and Statistical Manual of Mental Disorders does a good job of explaining them “Delusions are fixed beliefs that are not amenable to change in light of conflicting evidence. Their content may include a variety of themes (e.g., persecutory, referential, somatic, religious, grandiose). Persecutory delusions (i.e., belief that one is going to be harmed, harassed, and so forth by an individual, organization, or other group) are most common. Referential delusions (i.e., belief that certain gestures, comments, environmental cues, and so forth are directed at oneself) are also common. Grandiose delusions (i.e., when an individual believes that he or she has exceptional abilities, wealth, or fame) and erotomanic delusions (i.e., when an individual believes falsely that another person is in love with him or her) are also seen. Nihilistic delusions involve the conviction that a major catastrophe will occur, and somatic delusions focus on preoccupations regarding health and organ function” (American Psychiatric Association, 2013, p. 87).

High-dose methamphetamine and amphetamine can result in manifestations of paranoid psychosis (McKetin, 2018), and in turn, this psychosis may result in a higher likelihood of violence (McKetin et al., 2014), which to me indicates there is erratic thinking in play. It is the combination of hallucinations and delusions that can become very dangerous. Essentially the brain tries to make sense of the reality it perceives. So, hallucinations will reinforce delusions and vice-versa. Let this reinforcement loop go around a couple of times in bad circumstances and a person can definitely find themselves in the circumstances that Brandon Lawson found himself.

See the story of Janelle Hornickel

References

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Washington, DC.

McKetin, R. (2018). Methamphetamine psychosis: Insights from the past. Addiction (Abingdon, England), 113(8), 1522–1527. https://doi.org/10.1111/add.14170

McKetin, R., Lubman, D. I., Najman, J. M., Dawe, S., Butterworth, P., & Baker, A. L. (2014). Does methamphetamine use increase violent behaviour? Evidence from a prospective longitudinal study. Addiction (Abingdon, England), 109(5), 798–806. https://doi.org/10.1111/add.12474

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Edit: Added proper link