Fatigue during stressful times is very common and very normal.
I am responding to a question asked on this site, and I am responding with the assumption that the energy of the people asking was excellent before the stress occured. The reason being, that fatigue can be caused by a multitude of problems: low thyroid, low iron, low vitamin B12, low iodine, food allergies, acute and chronic illnesses that are diagnosed and not yet diagnosed, etc., etc., etc. (As well, stress can trigger, or aggravate these stated problems).
In a healthy person, with normal blood work and no existing illness, the following are helpful to improve energy during stress:
1) B-complex vitamins, including vitamin B6 (250 - 500 mg daily), and B5 500 mg daily (sometimes with people under extreme stress I give an intramuscular injection of vitamins B6 and B12)
2) Magnesium at least 500 mg daily and Buffered Vitamin C at least 4000 mg daily (if your bowels can tolerate that dosage)
3) LOTS OF REST and drinking 2 1/2 L of pure water daily
4) Rescue Remedy as needed (a bach flower remedy) for stress (and if grief is at all part of the fatigue/stress, then the homeopathic remedy Ignatia 30C can be helpful)
5) Astragalus (Chinese herb)
6) Siberian Ginseng
7) Licorice Root (only for those who don't have high blood pressure), preferably in a solid extract form (thick black syrup)
8) Eating really well, no sugar, no alcohol, no junk - maybe even juicing or taking a "Greens Drink". (I like the taste of Greens First myself).
9) Lots of meditating/praying/contemplating or whatever you do to connect with that which is bigger than yourself.
10) Seeing a massage therapist, or taking turns giving each other a 10 minute massage each day.
PS, I have found Mistletoe injections (Iscador) a wonderful therapy for helping prolong the life and quality of life in those with terminal metastatic cancer. (Among many, many other forms of therapy).
Of course, the info I've posted is not meant to diagnose, treat, etc. and that any questions should be addressed to your licensed healthcare provider.