Transmition slips from drive to neutral on its own

The transmission shift linkage or cable may be worn out or out of adjustment. This could cause it to just barely put the transmission into gear and not fully put it into this gear detent which helps to hold it in gear as well as the cable being in the proper position. So if this is the case a bump could knock it out of gear. Having it not shift into the detent fully is going to cause other internal problems if you don't get it fixed. You could end up with the clutch packs going bad and needing to rebuild the transmission. Since it is something that is automatic transmission related, I recommend you take great care in repairing it as it must go correctly into the detent which you can feel at the transmission with the shift linkage removed by moving the actual shift lever by hand. Otherwise I strongly suggest taking it to a transmission repair shop as opposed to a regular repair facility. This is because automatic transmissions are very complicated and take special expertise and tools that regular repair shops don't have. Try not to go to AAMCO as they are overpriced. The search engine on this site will help you find a transmission shop near you.