Hey
@Evil_Willy 
I'm sorry to hear you're facing withdrawals, that's never fun. My condolences for your being fat as all get out. I admire your honesty and confidence in saying so. You definitely beat me in that department, anywho onto your question.
It sounds like you've never had a terribly serious Opioid habit. In my day, it wasn't uncommon for someone to use 3g a day. On average, it was around 1g-1.5g for most people I knew including myself (at one point I did fuck up and found myself using quite a bit more than this).
It's really difficult to say how bad a person's withdrawal is going to be. We don't know you or what your drug usage looks like in your real life. If all we can do is have both of us guess, then you are the better judge as you know your body and mind.
Again, it sounds like you're not using too much right now. This is good. However, in my experience, using any Opioids for more than a few days had the potential to produce a severe withdrawal syndrome. I remember at one point, I had been completely clean for an extended period of time. This was about 10 years ago when the Heroin was Heroin. Someone gave me some Methadone pills, which I had never taken before at that point in my life. I ended up taking them for 3-4 days. I had a terrible withdrawal that didn't start getting significantly better until day 4.
At that point in my life, my knowledge of drugs was much more limited. Now, I know about the phenomenon known as the "Kindling Effect". The Kindling Effect in medical literature refers specifically to sedative/hypnotic drugs like Barbiturates, Alcohol and Benzodiazepines.
This effect implies that when a person becomes tolerant to say, Alcohol, then that person goes through withdrawal, the next time they start drinking, tolerance comes on faster, withdrawal hits harder and and you find yourself in the same situation that had taken you weeks, months or years to reach previously. It's really a bitch. Naturally, wider society is unaware of this. It creates some confusion. This leads to implications that a person has more or less decided to get back on drugs, when really, it's one seemingly insignificant mistake, that quickly becomes a runaway train.
I'm talking about the Kindling Effect as I feel it not only applies to sedative/hypnotics, but also to many other substances. We in fact know that the phenomenon translates to Opioids. I didn't get really dope sick for the first time until I had bee using for a few months. Now, like I said, if I were to use for 3 days or more, I could easily end up in a serious withdrawal.
An important question, are you experiencing withdrawal symptoms in between your Fentanyl usage? This would be a pretty good indicator of what you're facing. The experience of withdrawal is highly subjective. What some people might call a "nightmare flu" isn't the end of the world for me, as I've done it so many times, the fear and uncertainty aren't there, not to mention I have all of the coping skills I've learned throughout my addiction.
TL/DR I would hope for the best, but absolutely plan for the worst. I believe you will likely experience withdrawal for 3 days at a level at or slightly above your 0.25g Heroin withdrawal.
If you have questions regarding medications that help we can definitely give you some ideas. @negrogesic gave some really great advice as well.
