Your husband could be suffering from postural or orthostatic hypotension in which the blood pressure falls on standing up. Other than this it can be
hypoglycemia or vasovagal attack.
Since he also gets temperature fluctuations, the first things to be ruled out are thyroid disorders, adrenal gland problems, anemia, diabetes, hypoglycemia, liver diseases, low Vit B12, and vasovagal attacks.
Please consult your PCP for primary examination followed by proper referral.
Take care!