All the antidepressants and benzodiazepines can cause postural hypotension which may be exacerbated by BP meds. Certainly a warning would have been good, but since product information data have been included with meds many doctors have stopped explaining about side-effects. Which might just be nearly acceptable if not for the fact that many of us with anxiety disorders try to avoid reading about side-effects.
That said, I suspect that had you not taken either trazodone or lorazepam you still would have had about the same reaction because you jumped up from almost being asleep so the cardiovascular system has probably already begun easing down. At the small doses normally prescribed for sleep trazodone is not going to have much of an effect on the cardiovascular system, although it could at the 200-400mg needed to produce an antidepressant response.