Hey isedtoslink and welcome to Bluelight. Being that you're in the United Kingdom, you should be able to take advantage of the NHS in treating your addiction. I'm not positive what wait times are like for supportive medications like Buprenorphine/Methadone, but I know that they're available and are integrated into your health system. They should be fairly easy to access if that's what you're after. It's of course, a step you should only take when you're confident that you will not be able to maintain abstinence on your own.
I'm assuming you have a primary care doc assigned to you? The issue with Fentanyl withdrawal compared to Heroin, is that the withdrawal is relatively short and intense. Sure, it's great that it doesn't last as lone, but in reality, the intensity of the withdrawal can quickly incapacitate you and leave you unable to do the things you need to do to manage your symptoms. You can indeed be too sick to even get out of bed. I've been in bed for 4 hours thinking about getting up, but struggling with exactly how I'm going to do it.
If you don't have the presence to take control of your own symptom management, you run the risk of developing more severe and potentially dangerous symptoms like dehydration. Part of my withdrawal plan includes being able to swallow comfort medications and a limited amount of fluids, with electrolytes or just a pinch of table salt. Rectal administration isn't an option for obvious reasons, so I simply must be able to swallow without vomiting. If you can't do this, your situation will get worse quickly.
If you go see your physician, you can get yourself a little arsenal of comfort medications, potentially. You can wow your Doc by not asking for any controlled medications, which I'm sure he'll be expecting. To name a few, Gabapentin (Neurontin) for RLS/Akathisisa, Clonidine (Catapres) for heightened blood pressure/anxiety, Ondansetron (Zofran) an anti-emetic to enable you to swallow your other pills. With these three drugs, you will have a fighting chance at remaining in control of your syndrome.
As far as how long the withdrawal will last, I can only estimate. Opioid withdrawal in general is pretty linear and is actually pretty easy to describe and predict. Withdrawal from a drug like Heroin is going to last for ~72 hours acutely. Not taking into account half-lives or anything of that sort, I've always found Fentanyl to be maybe 70% of the duration of these drugs. Given this information, we can infer that your withdrawal phase might be ~50 hours of serious symptoms. Have you withdrawan from and Opioid dependency previously? If not, you need to educate yourself regarding Post Acute Withdrawl Syndrome (PAWS). I'm not going to sugar coat it. It's the phase after acute withdrawal in which you're not violently ill, but are still afflicted with depression, apathy, anxiety and lethargy. It's a bitch and you need to know that it's a huge factor in eventual relapse for many.
I would definitely hit your Doctor up, in short. Addictions to short(er) acting drugs are very hard to break. The high intensity and frequent peak/trough action of the drugs tend to make people scared, desperate and everything in between.
