An implantable medical device comprising: a sensing module; a therapy delivery module; a telemetry module and a processor; means arranged to detect an indication of a disruptive energy field; and wherein the processor is configured to: enter a disruptive energy field-compatible operating mode responsive to an indication of a disruptive field to be encountered by a patient in which the IMD is implanted, wherein the disruptive energy field-compatible operating mode is an operating mode in which therapy delivery is at least partially disabled, and which includes a first mode and a second mode; during operation in the disruptive energy field-compatible operating mode, detect a patient event based on data generated by the sensing module of the implantable medical device implanted, in use, in a patient; operate the IMD in the first mode in which the telemetry module of the IMD is disabled and the therapy delivery module of the IMD is at least partially disabled when the patient event is not detected; switch the IMD to operate in the second mode in which the telemetry module is enabled and the therapy delivery module is at least partially disabled, in response to the patient event being detected; and wherein, in the disruptive energy field-compatible operating mode, the processor is configured to operate the IMD in the first mode unless the patient event is detected. a sensing module; a therapy delivery module; a telemetry module and a processor; means arranged to detect an indication of a disruptive energy field; and wherein the processor is configured to: enter a disruptive energy field-compatible operating mode responsive to an indication of a disruptive field to be encountered by a patient in which the IMD is implanted, wherein the disruptive energy field-compatible operating mode is an operating mode in which therapy delivery is at least partially disabled, and which includes a first mode and a second mode; during operation in the disruptive energy field-compatible operating mode, detect a patient event based on data generated by the sensing module of the implantable medical device implanted, in use, in a patient; operate the IMD in the first mode in which the telemetry module of the IMD is disabled and the therapy delivery module of the IMD is at least partially disabled when the patient event is not detected; switch the IMD to operate in the second mode in which the telemetry module is enabled and the therapy delivery module is at least partially disabled, in response to the patient event being detected; and enter a disruptive energy field-compatible operating mode responsive to an indication of a disruptive field to be encountered by a patient in which the IMD is implanted, wherein the disruptive energy field-compatible operating mode is an operating mode in which therapy delivery is at least partially disabled, and which includes a first mode and a second mode; during operation in the disruptive energy field-compatible operating mode, detect a patient event based on data generated by the sensing module of the implantable medical device implanted, in use, in a patient; operate the IMD in the first mode in which the telemetry module of the IMD is disabled and the therapy delivery module of the IMD is at least partially disabled when the patient event is not detected; switch the IMD to operate in the second mode in which the telemetry module is enabled and the therapy delivery module is at least partially disabled, in response to the patient event being detected; and wherein, in the disruptive energy field-compatible operating mode, the processor is configured to operate the IMD in the first mode unless the patient event is detected.