I have absolutely no pleasure in the stimulants in which I sometimes so madly indulge. It has not been in the pursuit of pleasure that I have periled life and reputation and reason. It has been the desperate attempt to escape from torturing memories, from a sense of insupportable loneliness and a dread of some strange impending doom.

The speaker is saying that they have been taking substances (like alcohol, drugs, etc.) as a way to cope with difficult memories, feeling lonely and worrying about a potential disaster in the future. They mention that this has had a negative effect on their life and reputation. Basically they have been using these substances as a way of avoiding the pain they are experiencing rather than to have pleasure.