Holy laughter is a term used within charismatic Christianity that describes a religious behaviour in which individuals spontaneously laugh during church meetings. It has occurred in many revivals throughout church history, but it became normative in the early 1990s in Neo-charismatic churches and the Third Wave of the Holy Spirit. Many people claimed to experience this phenomenon at a large revival in Toronto, Ontario, Canada known as the Toronto Blessing.
Spiritual drunkenness refers to a phenomenon seen in some Christian denominations, particularly those associated with Pentecostalism and the Charismatic Movement, in which individuals who are said to be experiencing intense momentary visitations of—or even possession by—the Holy Spirit exhibit a range of behaviors resembling signs of moderate to severe alcoholic inebriation, including unsteadiness, uncontrollable laughter, silly expressions or gestures, verbal or nonverbal shouting (not typically in the form of glossolalia), sudden intense fatigue, and temporary unconsciousness. The phenomenon typically occurs during Pentecostal and charismatic church services, usually at the prompting of a preacher or pastor, and most often involving multiple members of a congregation at a time, generally after having been "transferred" from one person to another via respiratory blowing or laying on of hands.
The phenomenon has been videotaped, and after some searching I managed to find quite a few illustrative examples. Here are some: example 1, example 2, example 3, example 4, example 5, example 6, example 7, example 8, example 9, example 10, example 11.
Question: what is a psychological explanation for uncontrollable laughter and apparent symptoms of drunkenness in charismatic Christian congregations?
Possibly related question: Can a person be hypnotized to act drunk?
This is what I was able to find after spending some time on Google Scholar:
The Global Pentecostalization of Christianity and its Ethical Consequences (link)
A Kobylinski - Chicago Studies, 2016 - academia.edu
One of the phenomena typical for Pentecostal spirituality are psychosomatic symptoms, occurring during many prayer meetings in the form of convulsions, spasmodic laughter, or what is called resting in the Spirit. Andrzej Migda points out that, in the psychology of religion, such behaviours are classified as manifestations of “altered states of consciousness.” He believes that the “Pentecostal psychosomatic phenomena occur due to the same psychic mechanisms that enable shaman trances, walking on hot coals, or dervish dancing.” New members of charismatic communities are trained in achieving such ecstatic and mystical states.
I looked up Andrzej Migda, who is cited as the source of the claim, and found out that, according to https://pl.wikipedia.org/wiki/Pentekostalizm, he appears to be one of several Polish researchers who have investigated the Pentecostal movement:
The leading researcher of the Pentecostal movement was Walter J. Hollenweger (1927–2016), called "the founding father of research on pentecostalism." In his honor, in 2002 , the Center for Interdisciplinary Studies on Pentecostalism and Charismatic Movements was established at the Free University of Amsterdam . Hollenweger (Hollenweger Center for Interdisciplinary Studies of Pentecostalism and Charismatic Movements), which is a leading research center on this religious phenomenon  . In Poland, studies on pentecostalism are dealt with, among others, by prof. Zbigniew Pasek  , prof. Andrzej Siemieniewski , Dr. Edward Czajko , Dr. Leszek Jańczuk , Dr.Marek Kamiński , Dr. Andrzej Migda , Dr. Henryk Ryszard Tomaszewski or Fr. dr hab. Andrzej Kobyliński.
I then tried to search for peer-reviewed publications by these authors, but couldn't find anything conclusive about "holy laughter" or "spiritual drunkenness". To be honest, I am not aware of any peer-reviewed publication that has scientifically investigated the causes of these phenomena.