Research on the processes and effects of<unk>  is a subfield of neurological research. Modern scientific techniques, such as fMRI and EEG, were used to observe neurological responses during<unk> . Concerns have been raised on the quality of<unk>  research, including the particular characteristics of individuals who tend to participate.<unk>  lowers heart rate, oxygen consumption, breathing frequency, stress hormones, lactate levels, and sympathetic nervous system activity (associated with the fight-or-flight response), along with a modest decline in blood pressure. However, those who have meditated for two or three years were found to already have low blood pressure. During<unk> , the oxygen consumption decrease averages 10 to 20 percent over the first three minutes. During sleep for example, oxygen consumption decreases around 8 percent over four or five hours. For meditators who have practiced for years, breath rate can drop to three or four breaths per minute and brain waves slow from alpha waves seen in normal relaxation to much slower delta and theta waves. Since the 1970s, clinical psychology and psychiatry have developed<unk>  techniques for numerous psychological conditions. Mindfulness practice is employed in psychology to alleviate mental and physical conditions, such as reducing depression, stress, and anxiety. Mindfulness is also used in the treatment of drug addiction, although the quality of research has been poor. Studies demonstrate that<unk>  has a moderate effect to reduce pain. There is insufficient evidence for any effect of<unk>  on positive mood, attention, eating habits, sleep, or body weight. Moreover, a 2015 study, including subjective and objective reports and brain scans, has shown that<unk>  can improve controlling attention, as well as self-awareness. A 2017 systematic review and meta-analysis of the effects of<unk>  on empathy, compassion, and prosocial behaviors found that<unk>  practices had small to medium effects on self-reported and observable outcomes, concluding that such practices can "improve positive prosocial emotions and behaviors". However, a meta-review published on Nature showed that the evidence is very weak and "that the effects of<unk>  on compassion were only significant when compared to passive control groups suggests that other forms of active interventions (like watching a nature video) might produce similar outcomes to<unk> ". Potential adverse effects<unk>  has been correlated with unpleasant experiences in some people. In some cases, it has also been linked to psychosis in a few individuals. In one study, published in 2019, of 1,232 regular meditators with at least two months of<unk>  experience, about a quarter reported having had particularly unpleasant<unk> -related experiences (such as anxiety, fear, distorted emotions or thoughts, altered sense of self or the world), which they thought may have been caused by their<unk>  practice. Meditators with high levels of repetitive negative thinking and those who only engage in deconstructive<unk>  were more likely to report unpleasant side effects. Adverse effects were less frequently reported in women and religious meditators. Difficult experiences encountered in<unk>  are mentioned in traditional sources; and some may be considered to be just an expected part of the process: for example: seven stages of purification mentioned in Theravāda Buddhism, or possible “unwholesome or frightening visions” mentioned in a practical manual on vipassanā<unk> .
Meditation
Decapitation
Body substance isolation
Overtraining
Tightlacing
Seclusion
Complication 
Decompensation