I've been on 25-50 mg of benadryl nightly for 4 years. i've reduced the dosage to 12.5 the last few weeks. should i further reduce it, or quit all together? should i be worried about withdrawals, and what kind?

I don't see a reason to wean off this if it produces benefits to your life. Nightly use does not produce addiction like that found with narcotics nor does it trigger withdrawal when stopped. You may be mentally habituated and reliant to its use and benefits and if it helps, I see no reason to stop. Do as you wish. Some find a cup of chocolate milk at bedtime relaxing as a substitute.