What type of symptoms could one expect after being deprived of vitamin b1 for several years?

Many!: It depends on the cause. It can have serious consequences, too, especially in alcoholics. See https://umm.edu/health/medical/altmed/supplement/vitamin-b1-thiamine Get checked and see if you have it. Many of the symptoms can be reversed if caught in time.

Fatigue/stress: Isolated Vit B1 (Thiamine) deficiency is rare, but may cause the following symptoms: Headache Nausea Fatigue Irritability Depression Abdominal discomfort. Pl see attached link for an overview. In case of true deficiency, pl rely on your physician for authentic replacement with a reliable brand. Feel better!

Sooner than years: Thiamine deficiency causes berri berri, wet or dry, heart failure and neuropathy respectively. Deficiency lasting than more than a few months will produce central nervous system lesions, such as Wernicke's encephalopathy and death. See this site for more info: http://www.mayoclinic.org/drugs-supplements/thiamine/evidence/HRB-20060129