Major workup consists of ruling out treatable causes of<unk>  / delirium
Evaluate for precipitant of acute decompensation (e.g. infection, dehydration, MI)
Mini mental status exam
Six item screen
CBC
Megaloblastic anemia points to vitamin B12 deficiency
Normocytic anemia with an elevated RDW may indicated B12 deficiency as well if there are some RBCs with a small MCV and many with a large MCW.
Chemistry 10
LFTs
Urinalysis
ECG
CXR
ETOH
Urine toxicology screen
CT head
Consider
LFTs, TSH
B12, RPR, ESR, ANA, Folate, Thiamine, HIV
Neuropsych eval
Consider LP, urine heavy metals, EEG
Megaloblastic anemia points to vitamin B12 deficiency
Normocytic anemia with an elevated RDW may indicated B12 deficiency as well if there are some RBCs with a small MCV and many with a large MCW.
LFTs, TSH
B12, RPR, ESR, ANA, Folate, Thiamine, HIV
Neuropsych eval
Consider LP, urine heavy metals, EEG
Dementia
D = drug-induced
Delirium
E = emotions 
Normal pressure hydrocephalus
M = metabolic and endocrine issues
Parkinson's disease
E = eyes and ears 