I've had repeated, significant Vitamin D deficiencies, and yes, when it got severe, I've felt absolutely awful, so tired, it affected my stamina, mood swings, my bones hurt, muscle pain and cramps (Vitamin D deficiency can cause osteomalacia which I was suspected of, but they didn't do the other tests), I ended up having nearly every symptom of menopause to the point I was misdiagnosed with premature ovarian insufficency/early menopause for 5 years before it was connected to my deficiences.
The loading doses were transformative for me, I wouldn't say full health, but it was a major shift (I'd say 85% with just that) and as long as I continue supplementing as recommended, it stays that way. I know when I've missed too many doses, it messes with my cycles, moods, energy, pain.
I would suggest, if not already, having a wider nutrition panel if possible as it's pretty common to have more than one deficiency if only because a lack of one may mean another isn't being used or absorbed properly (bodies are complicated like that) and even more importantly, getting recommendations on how to supplement afterwards - once you've been significantly deficient, repeats are more likely and the best thing that happened in this for me was the last time, a nurse practitioner talk me through this - GPs usually just said take a multivitamin after the loading dose, the nurse talked through how much I should be looking for (multivits often don't have enough, especially for those with a history of significant lack) and foods to combine with it - just like Vitamin C helps iron absorb, Vitamin K works with Vitamin D so it's common to recommend having Vitamin D with natto, eggs, full fat dairy, or supplementing them together with 100mcg of K2 for every 1000ius of Vitamin D with 4x that regarded as safe without on-going monitoring (some say higher is safe, and a bit higher likely is, but the research in this area is pretty new). Some say Vitamin A up to similar levels of D is also helpful as the 3 work together.
If you're having bone pain or any other symptom of osteomalacia, you may want to look into calcium, phosphorous, and some say magnesium as well, if only to look for ways to increase them in your diet.