Ativan Side Effects. While most people tolerate Ativan well, it is possible for problems to occur during treatment. Common side effects of Ativan can include dizziness, weakness, and unsteadiness. A few other possible side effects include nausea, constipation, and fatigue. Some risks are more serious and require immediate medical attention; be sure to report side effects such as seizures or suicidal thoughts to your healthcare provider right away.