Yes it is true, you can experiance panic attacks....Some people may experience panic attacks (including extreme feelings of dread, accelerated heart rate, feeling as if they're going to die) from smoking cannabis, more commonly from those who have ingested too much then from smoking....


Most acute crises with cannabis are related to oral ingestion. Cannabis crises last 2-6 hours (or more) and can include paranoia, panic attacks, sluggishness, going in and out of consciousness, extremely bloodshot eyes, and mood swings. No deaths have been reported that did not involve physical injury. A few people reportedly have severe asthmatic attacks precipitated by smoking cannabis.
(Source: Erowid Psychoactive Vaults : Psychedelic Crisis FAQ)