Is early re-assessment common?

I have hijacked a couple of other post asking this but thought it better to start a thread.

I was assessed face-to-face 2012, placed in WRAG, appealed and was placed in the SG for 18 months). In accordance with this, I was sent an ESA50 nearing the end of 2013 and returned - with evidence (GP letter)- albiet limited as my condition is longstanding and I've not been under the care of any specialists since diagnosis).
I failed to provide evidence from my mum who helps me - she helps with care but does not claim carers' allowance / she works part-time - because she was dealing with stress, bereavement and a diagnosis of cancer in a very close relative, giving these reasons (this is all true but, also she crumbles when faced with speaking to anyone in authority, and I feared she may be somehow manipulated into saying I can do more (condition fluctuates)... I know they tried this with me at assessment so I wouldn't put it past them.
I also have a super helpful friend but I couldn't send evidence in from them as their young niece had just had a diagnosis of cervical cancer and I, quite frankly, thought it inappropriate to even ask under those circumstances.

In March 2014 I got a letter from DWP (assume it was a decision notice though it did not say that at the top of the letter). That was 3 months from having returned the ESA50. When I called DWP I was told the letter was my decision notice. I said it showed no date for reassessment and the man said that information is not disclosed in the letter, but that he could look at the system and tell me there and then. He said I was in the SG and that re-assessment was due after 3 years, I'd likely hear towards end of 2016 (ie ESA50) with a medical to possibly follow early 2017 based on my ESA50. I recall specifically asking if I were likely to be called before then and he said 'if your circumstances change ' which I took to mean they would revisit early if I provided info re a change of circs in the meantime.

I am now worried sick - esp as there was no f2f assessment the latest time, my evidence was by necessity limited etc that they may call me early. I didn't even know this was something that happened at all until I, by chance, read it in another post today. Does this happen often or do they usually need a reason to do this, call you before the designate time period is up?
I'm wondering if they are doing this because they couldn't fit in f2f assessments at the time...maybe I'm just being cynical.

Between those in the SG being called into JC+ for reviews and WRA despite being in SG, and this news (well, new to me) today, I honesty feel my illness is getting worse. My anxiety and stress is going through the roof and I can feel my symptoms actually worsening. Every day I suffer acute anxiety waiting for the post. My mum - still dealing with her brother's cancer, worrying about her mother's demenia, stress at her workplace, helping me, recently had a health scare herself, although, thankfully, she is okay - is getting worried about my state of mind (she sometimes can't cope and sometimes gets angry, though not directed towards me), and I'm feeling increasingly worried and
guilty about the effect my condition and increasing anxiety levels are having on her, she is not getting any younger.
This government (clearly) does not give a sod about people who are really ill. How on earth are we supposed to improve enough to work - where that's possible?

Sorry for about this message - I just feel so depressed and in a state about it all... I can't cope with the here and now, nevermind the what ifs and whens...

Thanks for listening.