not really a starter project, especially the TEXT message is not trivial.
Best advice I can give is to go first through the tutorial section to familiarize yourself with the Arduino and what can be done with it and how. (takes a week or two at most).
Then you should break up the project in smaller steps.
- investigate what sensors there exist to detect the person falling out of bed.
- detectors on the floor (think e.g. burglar detection, or IR movement detection )
- or detectors in bed (weight does disappear)
- probably you need a RealTime Clock (RTC) to see at what time it happens. SOmeone leaving the bed at 04:00 is different tha at 08:00
(and of course how to connect these to Arduino! .
Then you need to learn something about communication (wireless I think) to sent an event to another Arduino that will inform another person.
When you have more concrete questions, don't hesitate to ask.