I'm sitting on the lawn of the village church in Ticehurst, East Sussex, clutching a copy of the Tibetan Book of the Dead. In between swotting up on the hierarchy of the afterlife (the paradise of the gods, the realms of the demi-gods, men, animals, hungry ghosts and hell beings) I glance up at the passing snowy-haired gentlemen in crisp linen blazers talking of cricket, and they're starting to freak me out.

It probably wasn't a great idea to leave the Singing Rainforest sanctuary, a frosted-glass locale on the village high street, sandwiched between Cheryl's Dry Cleaning and CLeach the greengrocer.

When you're in the sanctuary, the altar – laden with wizened fruit and packets of Maldon sea salt, with a picture of a demented-looking god (Yamantaka, the Tibetan lord of the underworld) in the middle – begins to seem normal. Rain, my personal therapist and self-styled "Lunar Shaman Queen", has come to seem very normal too. Every so often she'll tell me what her "spirits" have been advising her to do before tonight's ayahuasca ceremony (flipping through Sacred Tibetan Teachings on Death and Liberation, for instance).

The plant she refers to as "Mama ayahuasca" is, Rain says, "the ultimate detox", because it "unblocks not just your body but also your mind and spirit from negative forces".

The good thing about 40-year-old Rain is that she's also got a great sense of humour, joking wryly that she's "the only black in the village". Her dad was a Ghanaian ambassador and she went to a girls' boarding school in West Sussex before getting a job in the music industry. And then, 13 years ago, she "woke up" – meaning that she found out that her great-great-great grandmother had been a revered healer in her native African village.

Rain believes that her ancestor entered the demi-god realm when she died and then went on to reside in the ayahuasca vine (believed sacred by all shamans who work with it). And through this she speaks to Rain.

I did an ayahuasca retreat this time last year in the Pyrenees; it was fun, and exhilarating, with a lot of 1970s-style album cover visuals – some of them profound and moving.

But Rain warns me that her ceremonies are low on visuals and heavy on "healing through purging". Vomiting is what she means, and she tells me the story of a journalist from a glossy magazine who came here recently, and whose vomit was filled with bad spirits. "The worst I've seen in years," she shudders. "I took a picture of it."

Sitting here in the churchyard, I worry if my sick is going to be photogenic. And then a snowy-haired lady walks past, talking about a "wonderful cream tea", and I start wondering what the hell I'm doing taking vomit-inducing hallucinogenics and tussling with "bad spirits" when I should just be having a nice, normal weekend in the East Sussex countryside.

Except maybe this village isn't so normal after all. Why don't the locals look you in the eye? And why are there goats grazing among the sunken headstones of the church graveyard?

Rain thinks that East Sussex has a Midwich Cuckoos vibe. "Devil energy," she reckons, adding that the mystic Aleister Crowley used to do ceremonies in the nearby Ashdown Forest and that the Scientologists and the Jehovah's Witnesses have their headquarters in the area. So I walk back to the sanctuary, figuring that maybe by this time tomorrow I'll know what the goats are thinking.

But this time around, the ayahuasca ceremony feels less weird – or at least less trippy. The "plant medicine" I drink has the familiar bitter taste, but it doesn't make me feel totally out of it. And Rain is a hard taskmaster. At one point, I start to feel myself fly up to some happy pink and gold clouds. But she steers me down, and soon we're in a psychodrama involving my family and ex-lovers and "bad forces".

At one point the lights on the ceiling become goats' eyes and I'm not sure what country I'm in, yet this doesn't bother me. I'm not allowed to mention too many of the family specifics, but at one point Rain's spirits tell her I have African blood. Then she starts vomiting – to get rid of my bad spirits, she says. I'm hoping this means I'm not going to have to vomit. But her great-great-great grandmother, it seems, has other ideas.

This is the gross bit. I hate being sick. But when some vomit finally comes, the lower back pain I've had for two months mysteriously vanishes.

We've been going for about four hours now and, exhausted, I drift into sleep. The next day I wander back to the graveyard. I feel light. I linger a while over a strangely beautiful spray of orange berries, and when I look at the munching goats there doesn't seem to be much difference between them and me. When one of the snowy-haired gents walks past I write in my notebook: "Sometimes you need to leave the cream tea world."

Back in London, I start to wonder if the stuff about bad spirits and swirling demons isn't actually mad at all. Well, maybe. I feel as though my system has been rebooted and the back pain hasn't come back. The only vaguely weird thing is that when I go for my weekly shop in Tesco I pass by the magazine stand and momentarily hallucinate that Peter Andre is a huge trout.

A detox that makes you see behind the face of C-list celebs? Rain's great-great-great grandmother probably knows what it all means.