Ever since my SCI, I have been using a heating pad during the day and and electric mattress pad at night because I need the heat to help me loosen up. If I do not have my electric mattress pad on at night, I feel like crap the next morning. I have seasonal allergies, but I am not really hindered by them. Sometimes, I take Benedryl at night so I can breath better. I have also taken Benedryl at night to help me sleep. The last two nights I have needed help sleeping so I took some Benedryl. Both times, I woke up the next morning feeling very achy and stiff. I found out that antihistimines, like Benedryl, reduce circulation.
I copied the line about "reduced cardiac output" from the article linked below my signature. I didn't read all of it. I just skimmed it until I found the cardiac statement.
Candle 
May there always be a light to guide you.
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Results indicate that intravenous
histamine produces tachycardia, systemic hypotension,
pulmonary hypertension, and reduced cardiac output.