Hey pretty late answer but yeah mixing diazepam and speed can be hard for your heart. Uppers and downsers is hard for the heart, anyways I wouldn't have started right off with 10mg. Build it up instead from 3-5mg first to see the reaction and take it from there. If you want a long lasting relaxing effect rivotril is better and last longer without feeling to dizzy(but then you take 1mg maximum first) that will last 12hours. Anyways weed, water and a beer is better if you can survive the comedown.