A chart in Wikipedia ("Indo-European vocabulary") [rearranged here] — see under "Bodily functions and states" — shows the connection between words for "sleep" and "dream" in IE languages, including Tocharian.
1. PIE: *swep- "to sleep", *swepnos "dream (n.)"
2. English: archaic sweven "dream, vision" (< OE swefn); NoEng sweb "to swoon" (< OE swebban "to put to sleep, lull")
3. Gothic: ON sofa "sleep (v.)"
4. Latin: somnus "sleep (n.)"
5. Ancient Greek: húpnos "sleep (n.)"
6. Sanskrit: svápnaḥ "sleep, dream (n.)"
7. Iranian: Av xᵛafna- "sleep (n.)" NPers xwãb- "sleep"
8. Slavic: OCS spěti "sleep (v.)", sŭnŭ "sleep (n.), dream (n.)"
9. Baltic: OPrus supnas "dream", Lith sapnas "dream"
10. Celtic: OIr sūan, W hun "sleep (n.)"
11. Armenian: kʿnem "I sleep", kʿun "sleep (n.)"
12. Albanian: gjumë "sleep (n.)"
13. Tocharian: A ṣpäṃ, B. ṣpane "sleep (n.), dream (n.)"
14. Hittite: sup-, suppariya- "to sleep"
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