i did a research project in insomnia and meds for it - both over the counter and prescribed..and i looked at non-pharmacological interventions - things like reading etc..
diphenhydramine hydrochloride is cautioned in the use of hepatic (liver) impairment..statins do much of their work in the liver, so it is possible that they might have a negative effect on each other.. but there is no contra-indications or warnings about the two together. i suggest you continue on the diphenhydramine hydrochloride if its working, but if you are worried or even just for reassurance ask your GP for liver function bloods every 6 months to monitor your liver..they may say its unnecessary, but if it will ease any concern then they should have no problem in doing it! and besides it doesn't cost them much to do it!
hope that helps.